The term 'cash register calculation' refers to the process of calculating the total cost of a purchase, including taxes, when using a cash register. This process involves four components: TAX (3 letters), tens (4 letters), ONES (4 letters), and RECEIPT (7 letters) and TILL (4 letters). TAX is the amount of money that must be paid to the government for the purchase. Tens and ONES refer to the denominations of currency used in the transaction. RECEIPT is the printed document that shows the details of the purchase, including the total cost. TILL is the drawer in the cash register where the money is stored.