Well, I have had such discrepancies at major banks, large chain quick service places (especially in airports), major hotel chains (especially in their F&B outlets, where this raises cash integrity issues), and many, many others over the past 13 years of MS. If the shopper catches it and reports it in the survey it is almost always okay; if not, questions will fly!
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.