Customer reveals not all tip percentages may be correct at pay machines

A customer at a popular restaurant noticed something about the tip calculator at the table pay machine- it was wrong. Every option of percentage of the actual total bill was off. Now, I’m not a mathematician, so if it looked right, I’d just pay it. But why? Was it because they’re accounting for the tax that the servers have to pay on their tips at the end of the night? Is it just a little kickback for the restaurant? Whatever the case may be, it sets a bad precedent because people might tip less since they don’t trust the system, thus affecting a server’s ultimate take home.