When I waited tables in college, we would cash out at the end of the night and enter the total credit card tips. You were also supposed to enter your cash tips. I believe the word then was that anything less than 8% tips of your total sales would be a red flag for the IRS. In a busy restaurant waiters don't keep a running count of their cash tips anyway and it's more of a guess at the end of the night. Servers tip out the bus boys, bar and food runners. The only time tips were split was behind the bar.