One page checkout not adding tax value to grand total in Magento .Cart page and checkout page showing different grand totals [closed]

Question

I have added discount from a custom module that I made.I am giving the observer's code below.Its working fine on the Cart page but tax is not getting added on Checkout Page. Getting paypal error: "PayPal gateway has rejected request. The totals of the cart item amounts do not match order amounts (#10413: Transaction refused because of an invalid argument. See additional error messages for details)." during checkout.

class Hs_Customcartdiscount_Model_Observer {

const XML_PATH_MODULE_ENABLE    = 'customcartdiscount/customcartdiscount_group/enable';
const XML_PATH_DISCOUNT_AMOUNT  = 'customcartdiscount/customcartdiscount_group/discount';

public function setDiscount($observer) {
    if(Mage::getStoreConfig(self::XML_PATH_MODULE_ENABLE)){
        $quote = $observer->getEvent()->getQuote();
        $quoteid = $quote->getId();
        $discountAmount =floor($quote->getBaseSubtotal()/100) * Mage::getStoreConfig(self::XML_PATH_DISCOUNT_AMOUNT);
        if ($quoteid) {
            if ($discountAmount > 0) {
                $total = $quote->getBaseSubtotal();
                $quote->setSubtotal(0);
                $quote->setBaseSubtotal(0);

                $quote->setSubtotalWithDiscount(0);
                $quote->setBaseSubtotalWithDiscount(0);

                $quote->setGrandTotal(0);
                $quote->setBaseGrandTotal(0);


                $canAddItems = $quote->isVirtual() ? ('billing') : ('shipping');
                foreach ($quote->getAllAddresses() as $address) {

                    $address->setSubtotal(0);
                    $address->setBaseSubtotal(0);

                    $address->setGrandTotal(0);
                    $address->setBaseGrandTotal(0);

                    $address->collectTotals();

                    $quote->setSubtotal((float) $quote->getSubtotal() + $address->getSubtotal());
                    $quote->setBaseSubtotal((float) $quote->getBaseSubtotal() + $address->getBaseSubtotal());

                    $quote->setSubtotalWithDiscount(
                            (float) $quote->getSubtotalWithDiscount() + $address->getSubtotalWithDiscount()
                    );
                    $quote->setBaseSubtotalWithDiscount(
                            (float) $quote->getBaseSubtotalWithDiscount() + $address->getBaseSubtotalWithDiscount()
                    );

                    $quote->setGrandTotal((float) $quote->getGrandTotal() + $address->getGrandTotal());
                    $quote->setBaseGrandTotal((float) $quote->getBaseGrandTotal() + $address->getBaseGrandTotal());

                    $quote->save();

                    $quote->setGrandTotal($quote->getBaseSubtotal() - $discountAmount)
                            ->setBaseGrandTotal($quote->getBaseSubtotal() - $discountAmount)
                            ->setSubtotalWithDiscount($quote->getBaseSubtotal() - $discountAmount)
                            ->setBaseSubtotalWithDiscount($quote->getBaseSubtotal() - $discountAmount)
                            ->save();


                    if ($address->getAddressType() == $canAddItems) {
                        //echo $address->setDiscountAmount; exit;
                        $address->setSubtotalWithDiscount((float) $address->getSubtotalWithDiscount() - $discountAmount);
                        $address->setGrandTotal((float) $address->getGrandTotal() - $discountAmount);
                        $address->setBaseSubtotalWithDiscount((float) $address->getBaseSubtotalWithDiscount() - $discountAmount);
                        $address->setBaseGrandTotal((float) $address->getBaseGrandTotal() - $discountAmount);
                        if ($address->getDiscountDescription()) {
                            $address->setDiscountAmount(-($address->getDiscountAmount() - $discountAmount));
                            $address->setDiscountDescription($address->getDiscountDescription() . ', Custom Discount');
                            $address->setBaseDiscountAmount(-($address->getBaseDiscountAmount() - $discountAmount));
                        } else {
                            $address->setDiscountAmount(-($discountAmount));
                            $address->setDiscountDescription('Custom Discount');
                            $address->setBaseDiscountAmount(-($discountAmount));
                        }
                        $address->save();
                    }//end: if
                } //end: foreach
                //echo $quote->getGrandTotal();

                foreach ($quote->getAllItems() as $item) {
                    //We apply discount amount based on the ratio between the GrandTotal and the RowTotal
                    $rat = $item->getPriceInclTax() / $total;
                    $ratdisc = $discountAmount * $rat;
                    $item->setDiscountAmount(($item->getDiscountAmount() + $ratdisc) * $item->getQty());
                    $item->setBaseDiscountAmount(($item->getBaseDiscountAmount() + $ratdisc) * $item->getQty())->save();
                }
            }
        }
    }
}

}

two screenshots of cart page and checkout page: cart page checkout page

Please someone help me.