Lest anyone think you will be tip poor in Europe, what TerryLynn did in the U.S. is generous beyond belief. In Italy, no one expects a tip for hailing a taxi. You will be seen as a rich American if you insist on doing this. As has been said many times before, rounding up the bill is sufficient in most cases at a meal. In a hotel, leave a couple of euros for the maid if you like. Round up the cab fare: €10.30 fare becomes €11.00. Nothing ostentatious.
At holidays or for people who serve you often, a little more generosity. We give three waiters that we see once a month all year €20 to €50 each at Christmas. When we want a table on a crowded July evening, they find us a place. When we stayed at a resort hotel for 5 nights over Christmas, at the end we tipped the three servers and one shuttle driver that helped us/served us the most and at that €20 each. That was a special circumstance.
I would not tip the private driver. MAYBE buy him one meal. That would be more than generous.
BTW, there is a year-end practice for private service people in Italy -= household workers and nannies -- and some companies do this too, I am told. They are supposed to receive a 13th month of pay at Christmas. I think restaurant workers receive this as well. Sort of a year-end bonus, a practice long gone in most of the U.S.