How much do I owe you?
DE-ve — two syllables, stress on first.
After being served at the bar when you want to pay. More informal than 'quanto costa' — assumes a service relationship.
'Mi deve' literally means 'you owe me' — but in this context it means 'how much do I owe you'. It is a common, slightly informal way to ask for the total. The barista will tell you the price and you pay directly at the bar.
Quant'è?
How much is it?
Even shorter — contraction of 'quanto è'. Very casual but widely used
Pago adesso?
Do I pay now?
Confirm whether to pay immediately or at the end
Tenga il resto.
Keep the change.
If you want to round up — a common way of leaving a small tip at the bar
Leaving the coins as a small tip by saying 'tenga il resto' (keep the change) is the standard Italian way to tip at a bar. It is not expected but appreciated. Rounding up to the nearest euro is the most common version — nobody tips at the bar the way they do in restaurants.