I had no idea when I went to Japan that change trays existed outside of restaurants, or that they would be used in every cash transaction I would make in Japan. But they were. My first slightly awkward experience was within a very short time of disembarking my flight. The JR ticket office at the airport, buying Suica travel cards. When I went to hand the cashier cash, she looked at me, smiled and extended a plastic tray with a rubber mat at me. I was a bit confused. I worked out very quickly that you place the money on the tray, always.
Just another aspect of Japan’s highly stylized etiquette, this tray ensures a number of potential problems are eliminated. Firstly, no-one has to touch strangers (this could be embarrassing and troublesome). Secondly, the money is very visible and easy to count, thus ensuring no problematic discrepancies. Thirdly, most Japanese think it is more polite to give and receive money on the tray. And finally, it removes the embarrassment sometimes associated with dealing with money (giving or receiving).
I personally find the trays are a God-send, when you have a wallet full of 1¥ coins. It enables you to count out your cash, without dropping it everywhere, or losing track of what you’re counting. Also worth noting is that you do not need to get flustered and panicked while paying. Most Japanese are very tolerant of a job being done well or properly, so counting out the correct change is fine. (Even when you take a long time, because you’re trying to work out which coin is which!)
Image credit: http://www.123japanese.com