Aaron Parecki

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. :)

I don't round down. If a gas station can charge 9/10ths of a cent per gallon the restaurant's pos should be able to go to 4 decimals.

I always write the tip amount! I assumed if I didn't the cashier would have to do the math instead. Easier for 150 to do it once than one person do it 150 times. And yeah, I also decshift, round down, multiply by two. Reliably 19-20% tip, but no checksum.

you write the tip amount on the receipt? I just always write the total amount.

My algorhythm for tipping prioritises speed so I just allow for a margin of error. We can adjust for it in the mapreduce before cold storage. And I try to obfuscate the tip to prevent alterations. So far so good.

Left shift decimal 1 place the multiply by 2.

This gets tricky when prices are either large or end in strange decimals (sales tax):

Pre-tip bill: $81.12
Rough tip: $16
Pre-checksum total: $97.12
9 + 7 = 16 (?)
Final: $97.16 (last digit of sum = 6)

Adjust up to $16.04 or down to $15.94? The mental math could trip people up.

:-O

That was a bad example. Last time this happened, my $5 tip was changed to a $15 tip.

why? Unless they change it to like 100% or something wild, let em have it. Likely they need it if they go to the trouble