Before adding a cash discount to your store please speak with your credit card processor about rules and regulations in your area regarding this.
To add a cash discount to your store you must follow these steps:
1. Log into the back office.
2. Go to settings, then store settings.
3. Using the tabs up top select service charge.
4. From here you will add a service charge to each card option. (you can do this by clicking the add service charge button)
5. Click save.
Please note that the cash discount is the total amount on the check.  When you use any card it will apply a service charge equal to the percentage that you set.