Keep the change.
'Tenga' — 'TEN-ga'. This is the formal imperative of 'tenere' (to keep).
Use when paying and you want to leave the extra amount as a tip without having to explain.
'Tenga' is the formal imperative of 'tenere' meaning 'keep'. 'Il resto' means the change. It is among the most useful phrases for any Italian payment situation. Tipping taxi drivers is not obligatory in Italy but is appreciated.
Lasci perdere il resto.
Forget about the change.
Equally natural alternative; 'lasci perdere' means let it go.
Arrotondi pure.
Round it up.
Asks the driver to round up to a convenient figure for the tip.
Quanto le devo?
How much do I owe you?
Asks the total before deciding on a tip.
Tipping taxi drivers in Italy is not as ingrained as in the US or UK. A common practice is to round up to the nearest euro or two. For airport runs or long journeys, €2–€5 is a generous and appreciated gesture.