Which button should be pressed to void the last sale?

The button that should be pressed to void the last sale is the one labeled 'Void.' This option is specifically designed to reverse or cancel a transaction that has already been processed. In retail and point-of-sale systems, the 'Void' function typically handles this operation directly, ensuring that the sale is appropriately undone in the system's records.

This action is critical in maintaining accurate accounting and customer transaction histories, as it reflects the need to correct errors or address customer requests after a sale has been finalized. Utilizing the 'Void' button simplifies and streamlines the process for both employees and customers, as it communicates clearly that the intention is to completely retract the sale rather than simply cancel a pending action or process.

While other buttons like 'Cancel' might suggest stopping a transaction, they do not specifically indicate the intention to void a completed sale. Similarly, 'Last' and 'Enter' relate more to recalling or confirming actions rather than reversing a transaction. Thus, pressing the 'Void' button is the most appropriate choice in this situation.