I used to work in restaurants as well; as a manager. Each server was responsible for collecting their checks whether it was paid in cash or by card. At the end of the day, we collected the receipts, compared it to the amounts listed on the computer, deducted the card receipts and collected the remaining checks at one time, so the restaurant's till would be 100% accurate, as the server paid what was owed in cash and kept the rest as their tips. So the server could make out like a bandit if (s)he was shortchanging the customer and receiving extra money for tips.