There is no custom of tipping in Japan. There isn’t but… Sometimes we give money as a sign of gratitude when we received special consideration or care.
For instance, when attending a wedding, we would tip some of the staff who took great care of us, or if we stayed at an inn or a hotel, we would tip the housekeeper. The situation varies, so call to action differs. The latter example of tipping is mainly seen when people from overseas come to visit.
It is an expression of appreciation or gratitude for a favor. There is no obligation to give a tip, and even if you didn’t, it would not be offensive. Of course, if you are satisfied with the service, we’re sure it would be appreciated. However, there are also cases in which we have a policy of “politely declining,” when staff will refuse to take a tip. In this case, do not be offended by any means. Just think, “Oh, this level of service is expected at this location”.
By the way, when giving such tips, we recommend putting it in a small bag or envelope. It is often called a “Pochi bag” and different from “Go-shugi bag (celebration bag).” Actually, there are many kinds of these bags. There seem to be a lot of people buying these for souvenirs, too?