Usually a regular computer (if with lots specialized software), with a keyboard. Not a cash register, the drawers are physical locking drawers in a cabinet. No speakers or sound. Some tellers are behind bulletproof plastic, so it’d be quieter still. Use the mouse or keyboard shortcuts to go into something like Payments --> Credit card, and type in the data. The “No sale” button is called the ESC key multiple times. Voided transactions are saved, as are all completed transactions (pseudo-screenshots of everything). So faking it that way wouldn’t work, although I suppose you could click random things.
But IME, there are also about 2 dozen cameras behind you, so as I said if they come back and report it soon after, odds are higher that they can figure something out. 2-3 weeks later? Yeah, odds are low. But I’d hope the manager would at least look into it. So not saying it can’t happen, but it would be a solvable problem, if done in a timely fashion.
Oh, and although we were allowed to have our wallets on us, taking them out was a no-no. Even if it was after hours and you got a sweet-ass Grover Cleveland dollar you want to take home, the right way was to trade with another teller and buy it off them with your personal money.