I need to display (tier) prices based on the qty increments of a product. E.g. a simple product, with a regular price of 50¢, no taxes and qty increments of 20 should be displayed on product views with "$10 per 20". Without using taxes this should be quite easy. But there seems to be no "default" helper or model to do this with taxes enabled and different calulation algorithms (e.g. Mage_Tax_Model_Calculation::CALC_UNIT_BASE); expect for quotes in Mage_Tax_Model_Sales_Total_Quote_Tax and Mage_Tax_Model_Sales_Total_Quote_Subtotal. Did I miss something here, or do I have to write the business logic on my own? And how I would best encapsulate it?