Is there a preferred way to implement discount codes?

[formidable01]

When using the PayPal API, PayPal itself does not have a discount code interface so it must be implemented as part of the front-end before PayPal gets the payment amount. Is there a preferred manner to implement this function within django-payments?

[WhyNotHugo]

Personally, I already had these implemented before migrating to django-payments. My Order model handled discounts and the total_price was the subtotal minus discount. So my payment model gets the total minus the discount.