Tipping.
If the service is good and you want to tip, then a reward of 10% is sufficient once you receive your change in a bar or restaurant in Poland.
A note of warning though – if you say “thank you” after the waiter collects the money for the bill this will be understood as “keep the change”. Tips are left once you have already received your change.
In a taxi, it is usual to just round up the fare.