Was just in Japan and encountered these everywhere. We knew to use them from our research prior to the trip. Initially I was under the impression it was to prevent the spread of germs, but that didn't really line up because the money comes into contact with the cashier's hand regardless if the tray is used or not. I guess it could help reduce the amount of small hand-to-hand contact that is sometimes experienced when you place money in someones hand directly.
It was easier for the cashier to glance at the amount we had placed in the tray and help us count out the correct amount of money for our first few days there while trying to get accustomed to the types of currency.
Also, it's visual in the sense that both parties can easily verify that it is the correct amount and avoids any "…but I thought I gave you five quarters…".
It was easier for the cashier to glance at the amount we had placed in the tray and help us count out the correct amount of money for our first few days there while trying to get accustomed to the types of currency.