I currently have 3 groups, Group A which tax applies to and the other 2 (Group B & C) which tax doesn't apply.
I would like to know is it possible so that when not logged in or logged in as Group A the prices are displayed with the tax applied everywhere. However when logged in as Group B & C the prices are displayed without tax everywhere?
I do not think this is possible out of the box but then class Mage_Tax_Helper_Data has all the functions to do with display prices with or without tax. For example displayPriceIncludingTax and displayPriceExcludingTax, though there are more.
What you could do is rewrite this helper and change these functions to match your need. Though tax display is a slippery slope so make sure you test this a lot :)
It would seem its not natively possible.
However looking at
This provides a solution but ideally it would of been better to give the admin the choose in the backend rather than hardcoding it in
public function getPriceDisplayType($store = null) { $customer = Mage::helper('customer')->getCustomer(); if ($customer->getGroupId() > 1) { return self::DISPLAY_TYPE_BOTH; } else { return (int)Mage::getStoreConfig(self::CONFIG_XML_PATH_PRICE_DISPLAY_TYPE, $store); } }