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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Total pre-tip bill: $15.90 Rough tip: $3.00 Pre-checksum total: $18.90 1+8 = 9 Final total: $18.99 Now if someone changes the tip to $4 or $5, the checksum fails.

Jul 19, 2018 · 11:12 PM UTC

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Replying to @aaronpk
Maybe easier version: adjust the tip so the dollars & cents of the total are equal. Then you make sure all restaurant charges on your credit card statement look like $18.18 or $7.07 or $123.23. Less subtle but realistically probably plenty subtle unless this really catches on. :)
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That was a bad example. Last time this happened, my $5 tip was changed to a $15 tip.
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you write the tip amount on the receipt? I just always write the total amount.