This is a cash cache. Bring your coins and $1 bills!
If you find a penny, take it and leave a nickel.
If you find a nickel, take it and leave a dime.
If you find a dime, take it and leave a quarter.
If you find a quarter, take it and leave a dollar.
If you find a dollar, take it and leave a penny.
At any point in time, the cache should only have one coin or one dollar bill. If you should find multiple coins, take all, except for the one with the highest value.