Used by GIs in forward bases area of combat zones, and used dollars to purchase PX items like potato chips, etc that cost less than a $1. The change is returned in cardboard circle gift coins like the one you show. If a GI left the change in his uniform pocket there is no rattling of coins in the event the soldier was dispatched to a forward point on short notice. Sort of like silent paper chips used in back rooms so a game made very little noise of chips splashing a pot.