just a few days ago, i encountered a receipt that included "suggested tips" with 15% and 20%. but whatever the numbers were, they weren't 15% or 20%. i could not find any permutation of the total (pre-tax or post-tax, with or without drinks, and randomly excluding an item) that would make a total that matched the suggested 15% tip.

has anyone else encountered this before - where the precalculated "helpful" tip amounts are not the percentages they claim to be?