[Done v1.3.9] Sales Tax Calculation Incorrect

[fergusmacdonald]

I've just posted a comment on the Quantity Discounts support thread regarding a tax calculation error:

http://www.zen-cart.com/forum/showpo...&postcount=389

However, i've realised that this error occurs when any discount module is used, including the inbuilt Discount coupons.

The tax appears to be calculated on the subtotal rather than as a percentage of the total. There are a number of other threads with similar problems:
http://www.zen-cart.com/forum/showthread.php?t=94942
https://www.zen-cart.com/forum/showthread.php?p=706968

I'm not a coder so cannot say how this is calculated but it would appear that when a discount coupon is used, tax should be calculated based on the order total (excluding the shipping amount if there is no tax on shipping).

Any help on this problem would be much appreciated.