About 10 years ago I had a second job at a gas station and someone came in and paid for junk food with proof coins...Ikes, Bicentennial halves and quarters.
I have also found a 1938 Swiss 10 Rappen, 2008 Mexico Peso, 2000 Somalia 5 Shilling FAO, and a Philippine 5 Centimo in circulation.
I used to search all denominations 1c thru $1 back in 2005, 2006 compiling complete modern sets from circulation. Wheat Cents were 1 in 150, so the 1/2% figure given a few posts above rings true as they are likely closer to 1 in 200 being several years later now. Found one Indian Head Penny out of probably 10,000. Got one dateless, tired Buffalo Nickel out of probably 10,000. Found a couple Silver Dimes out of several thousand. Found one Silver Quarter out of about 10,000. Don't remember seeing any Barber coinage. Pretty sure I got a few circulated Walkers. Never any Dollar earlier than 1971. The Half Dollar searches were always fun and interesting. Got some that had Silver streaks in them; some had stuff that weren't even coins but must've been designated as Half Dollars by the coin counters. These included Foreign coins, guitar picks, and other weird small trinkets. Back when I was roll searching, Washington head quarters were about as common as Statehood Quarters. I wonder what that ratio would be today? The ratio of Washington head to statehood to ATB would probably be about 20% to 60% to 20% would be my guess based on what I receive in change today. Let's be honest, though, Half Dollars don't really circulate any more. Small dollar coins hardly ever DID circulate. This is a shame. Should be exactly the opposite as inflation pushes higher, you have to have 50c or $1 for a coin to have buying power. Quarters do still have some buying power. But dimes, nickels, pennies are kind of a nuisance that get sent off to the change cup or jar or bucket until you cash in at the bank. Coins aren't used by the general populace at large because of inflation, failure to get rid of paper dollar forcing dollar coins to actually circulate, not introducing higher denomination coins, and credit cards and bank wires being more popular than ever. People just don't use cold hard CA$H like they used to; so much is on paper. This is the topic that caused me to go from lurker to member. How's this for a first post