Annnnnd to complicate matters there are credit companies won't allow businesses to do a "minimum transaction" policy which is why some smaller, local venues won't go electronic. One thing I have seen a local gas station get away with is charging a few cents less per gallon on gas that is paid for in cash. I don't know how kosher that loop-hole is.
But this is also why you get businesses that won't use certain credit cards like American Express; they charge a higher rate than visa/mc.

/end learning