From your 'My Hub' page (please see below)
On the left hand side of your account, you will see the side menu in which you can select 'Financials'.
Simply click the 'Receipts' tab from the 4 options at the top of your page.
You can then create a receipt by hitting the 'Create Receipt' button at the bottom of your page
Where you will be able to add all the details of the purchase including whether it was a 'Cash' or 'Cheque' payment