change oder totals after change tax item order magento 1.9

Question

I have add an observer to sales_quote_collect_totals_after to changing tax amount, the tax is changed but order totals and tax totals are wrong. I tried with :

<checkout_submit_all_after>
            <observers>
                <Module_Sales>
                    <type>singleton</type>
                    <class>Module_Sales_Model_Observer</class>
                    <method>setTaxAmountOrder</method>
                </Module_Sales>
            </observers>
        </checkout_submit_all_after>

Without success finally i try to change the totals by :

 $order = Mage::getModel('sales/order')->load(356);
 $order->setSubtotal(500) ;
 $order->setBaseSubtotal(500) ;
 $order->setGrandTotal(500) ;
 $order->setBaseGrandTotal(500) ;
 $order->setBaseSubtotalInclTax(500) ;

Without success because only setSubtotal has changed. Can you help me.

this is when i save order

$_items = $order->getAllVisibleItems();
    foreach ($_items as $item) {
        $price = $item->getPrice();
        $basePrice = $item->getBasePrice();
        $_taxHelper = Mage::helper('tax');
        $_store = $item->getProduct()->getStore();
        $_convertedPrice_ = $_store->roundPrice($_store->convertPrice($item->getPrice()));
        $_convertedBasePrice_ = $_store->roundPrice($_store->convertPrice($item->getPrice()));
        $taxamount = $_taxHelper->getPrice($item, ($price * 0.2), null, null, null, null, null, null, false);
        $baseNewTaxAmount = $_taxHelper->getPrice($item, ($basePrice * 0.2), null, null, null, null, null, null, false);
        $finalprodprice = $_convertedPrice_ + ($_convertedPrice_ * 0.2) + ($taxamount - ($item->getProduct()->getPrice() * 0.2));
        $finalprodBaseprice = $_convertedBasePrice_ + ($_convertedBasePrice_ * 0.2) + ($baseNewTaxAmount - ($basePrice * 0.2));
        $item->setTaxAmount($taxamount - ($item->getPrice() * 0.2));
        $item->setBaseTaxAmount($baseNewTaxAmount - ($item->getPrice() * 0.2));
        $item->setPrice($finalprodprice);
        $item->setPriceInclTax($finalprodprice);
        $item->setBasePriceInclTax($finalprodBaseprice);

        $item->save();
    }
    $order->setSubtotal($finalprodprice)->setBaseSubtotal($finalprodprice);
    $order->setGrandTotal($finalprodprice)->setBaseGrandTotal($finalprodprice);
    $order->setBaseSubtotalInclTax($finalprodprice);
    $order->save();

Answer 1

For those how has the same problem, the execution of my module where not the last their is another module how is executed the last by the observer. i rename my module with the first lettre Z .Now my module is executed the last because the order of execution is alphabetic.