Round off. If the bill is whole numbers, add a little something if you feel it was worth it.
Taxis – how much did they add on for the luggage? Was it a nice ride? Shuttles – you paid a price that should include the tip – Do not feel guilty not leaving a tip -
In a restaurant, if you liked the server, add an euro or two. In the taxi, round off. In the shuttle, give an euro or two if the driver was helpful with hints.
In a café if you leave loose change, that is fine; nothing, that is fine because the 15% cover is included in the price. We generally leave about 30 cents or nothing.