It isn't the cash, it is the principle of the issue. My godfather talked about how before the '50s, how grocers would stick a thumb on the scale, return change for a $5 when one paid with a $10, then dared the customer to make an issue out of it, and so on. If one doesn't do something, then this behavior is just encouraged. A thief is a thief, weather it be someone stealing a quarter off a bar counter to put in a jukebox or driving off in a car with keys in the ignition.
About a year ago, Visa lost a court case that prohibited credit card merchants from having tiered pricing structures. However, some states (definitely Texas) have put their foot down. Other states allow up to a 5% credit card surcharge. This has caused a number of issues, and oftentimes, merchants don't post the surcharge notice, surprising people in the states that do allow it.