With the GF eCommerce Fields plugin you can easily add eCommerce field types to your Gravity Forms. The new pricing fields include Discount, Tax, and Subtotal. This plugin also improves upon the functionality of Gravity Forms’ Coupons and Shipping fields. GF eCommerce also adds support for special merge tags for including the subtotal, coupon and discount amounts in calculation-enabled fields along with a handy merge tag for displaying the order summary in your confirmations and notifications.