It's better to leave nothing. Tipping a private driver in Italy depends on the quality of the service and the amount of time involved. If it's a short drive to the hotel, than tip like you would a taxi. If it's a full day's tour where you driver is also a guide, then 10% is good.

In Italy, tipping a driver is not mandatory and is generally less common than in the United States, but it is appreciated for exceptional service. For a standard taxi ride, most locals simply "round up" the fare to the nearest euro or leave an extra €1 to €2 if the driver was helpful with heavy luggage or navigated a particularly difficult route. For a private transfer or a pre-booked car service (e.g., from an airport to your hotel), a tip of €5 to €10 (or about 10% of the total fare) is appropriate for a high-quality, professional experience. If you are using a ride-hailing app like Uber Black (which is primarily what's available in Rome and Milan), you can add a tip through the app, but even there, a small amount is sufficient. Italian drivers do not expect a tip as a matter of course, and the service charge is often theoretically included in the price. A simple "grazie" and rounding up the change is the most authentic "local" way to show your gratitude for a job well done.