To see a log of all sales go to Downloads → Reports → Logs and choose Sales from the dropdown list. This will give you a report that looks something like this:
The user column lists the customers names. If you click on a customer name it goes to their personal payment history.
The Download column shows what that customer bought. If you click an item it filters this page to show only that Download. You may also filter for any product using the second dropdown list.
The Payment ID is simply a unique ID for that payment. If you click one it goes to the details page for that transaction.