I have had Amex correct my addition. Yes, sometimes I'm too clever by half to get a whole number or multiple of $10, and make an error.

I'm more likely to complain to a manager about bad service than leave a punitive tip. I'll also speak to the manager about kitchen issues rather than taking it out on the server.

Any attempt by the server or restaurant to write in a larger amount is simply fraud and I would report it without hesitation.