In France, no tip is necessary, but it is common practice to round to the nearest 5 or 10 EUR. Many restaurant menus in France say "service compris" on the menu (means service included), so they are not expecting a tip anyway. If the service was exceptional 5% could be added.
Staff in the service industry in France have a different wage structure to, for example, the US and they are not reliant on tips to make up the rest of their salary.
At DLP, we always book restaurants to the room bill and there is no need to carry cash. Prices at DLP are very high to cover all costs including staff wages and service.