In my state an employer is only responsible for raising an employee's effective wage (for the entire pay period) to minimum wage if the tips don't.
You can tip someone working as a waiter $100 and unless they've already hit minimum wage for that pay period, all you're doing is handing $100 to the owner because it's $100 they don't have to pay in wages. Once the waiter has met minimum wage, then the money actually goes to them.