Tax Issue

We are having a tax issue on our site, yes I know we need to update our word press version and we are working on that. The issue we are having is that the tax is being applied before a discount is applied. So that means if someone has 4 products in their cart the tax is hitting the subtotal which is fine if the customer doesn’t have a discount code to use. If they have a discount code to use the tax is going off the full price, not the discounted price, thus the charging too much tax.

We are using the Gold Cart plugin with our WP eCommerce. Please let me know if there is anything I can do to fix this.