Tax Calculation Basis

Problem Description --------------------------- According to New VAT law just passed by Egyptian government applied from 7-9-2016, we have new business requirement as following: Need to calculated the tax"Tax Event" based on line amount before any modifiers applied as below example

Line Ordered Item                       Qty             UOM            Unit Selling Price                         Extended Price                 List Price                  Discount Tax                    Amount

1.1 1122010201001                   100               EA                      7.21                                         721                                7.43                           22 57.68                                                                  Currently Behavior Tax Rate * Extended Price New Requirement according to LAW  need to calculate according to this equation (Tax Rate * List Price * QTY ) This needed for specific tax classification codes not all.

How to handle this issue to meet this requirement