We can create return discount coupons that are flat rates (ie $10.00) where the customer returns to the store after making their purchase and uses the bottom of the receipt as a coupon for that value. However we want to change it from a flat rate to a percentage of sales. 

Example: 

Total amount: $380.00

Percent discount: 10%

Total coupon: $38.00

See below for my attempts at making this work. If anyone could verify that this coupon will do what I need it to do would be greatly appreciated.