How Promotion Discounts Are Applied to Transactions
Discounts are applied to a transaction automatically when a promotion is applied. The value of the discount is dependent on how tax is calculated in your region.
By default, promotion discounts are applied to the transaction total after sales tax has been calculated. However, in the U.S. you have the option to apply the discount to all items in a transaction before sales tax is calculated. For more information, see Applying a Discount Before Sales Tax