I used to work with a Greek-American (he had emigrated from Greece as a teenager, and later became a naturalized American citizen) who frequently revisited his home country and always brought back plenty of Greek coins.
I don’t recall all of the different currency values (coins worth various numbers of drachma), but I do recall that the drachma was a very much less valuable unit of measure than the US penny. He explained to me why he brought back so much apparently useless currency to the States. If he had a coin that was worth, say, 25 drachma and had the approximate size and weight of a US quarter-dollar (a quarter, in other words), then the Greek coin was worth considerably less. It would never fool even a half-awake cashier, but apparently it would always fool the automatic toll machines on Chicago’s Northwest Tollway. So where others had to pay 50¢ at a toll booth, he could get away with paying something like 8¢ by using various Greek drachma coins to fool the machines. Not exactly counterfeiting, obviously, but illegal, of course.
What the Illinois Toll Road Commission did with all of the Greek drachmas that they must have collected over the years, I have no idea, but whenever I receive change for any transaction in the Chicago area (especially at toll booths), I always examine it now.