Outside Japan a sum of money left by a customer as a sign of gratitude for received service, is called a tip.
However, here in Japan, leaving tips is often seen as something suspicions, and in many cases money are returned without being accepted.
To non-Japanese this can appear to be confusing, but this is actually is a kind of Japanese national trait.
In Japan, especially in service industries, there is a specific concept of Japanese hospitality towards customers. This is the spirit, that can be explained as “taking actions that are aimed at satisfying customers is a natural thing to do”. If such actions towards customers are not performed, this would be equal to being impolite.
Tips are often left by customers in hotels and restaurants.
However, in Japan there is no need to leave any extra-payments. In case you left tips as a･･･