Adding A Custom Discount Order Total in Magento Does Not Change Sales Tax

Question

I have created a custom order total that gives a discount in certain situations. The grand total always comes out correct, however the sales tax calculation is not taking my dis

Answer 1

Go to System > Configuration. Select "Tax" from the left hand navigation, then open the "Calculation Settings" group if it isn't already.

Try changing the "Apply Customer Tax" parameter to "After Discount"