From your 'My Hub' page (please see below)
If you go to the 'Menu' icon in the top right...
then select 'Financials' from the options
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