[cptskippy]

Actually what you've done is devised a system for you to steal you staff's tips.

Instead of customers having the option to pay extra in the form of tips, you're charging more. By having a review/bonus system, you're still absolving yourself of the responsibility for fairly compensating your staff. You're shifting the burden of evaluating employee performance onto your customer. And you're incentivizing yourself to limit bonuses because that money goes into your pocket.