Unlike in other countries, there is no obligation to give tips to the restaurant staff. In every drink and meal, a share for their salary is already included / calculated.
However, as they definitely do not get rich with their salaries for a sometimes stressful job, a tip is always welcome. The least you can do: Add the sum up to the next Euro-value; e.g. EUR 12,40, make it 13 EUR. If you pay with three
Angelina and me, we give around 10% of the sum if they are good and friendly, and at least in our preferred restaurants, they usually are.
So, choice is up to you - a tip is always welcome but you are not obliged to give one.

