Purchases made in your site can be found on the Site Orders page. To view your Site Orders page, go to Admin Tools, then under Reporting go to Site Orders.
The overall Site Orders page lists every purchase made in your site, be it for course or membership purchases.
Orders where an individual used a coupon will also appear on this page, even if the usage of the coupon makes the order free.
Selecting the Transaction ID allows you to view details about that order, including who placed the order, the order date, status, total, courses purchased, and coupon code used (if one was used).