Started using the last digit of my restaurant bill as a checksum, cause I've had the tip amount changed on me too many times now
Decide your rough desired tip, calculate your tentative total, then add up the digits before the decimal point and use that as the number of cents
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aaronpk_tv
Interesting way to catch tip modifications by waiters. However, I am always surprised that in this age of digital everything, where even currency has gone digital, we are still forced to depend on scam-prone manual tip checking.