I used cash at the toll booths in Italy but as I recall there is a plastic option.
It sounds like Switzerland uses a system like Austria, you buy a sticker to drive your car on the highways. Since it's a rental, the sticker may already be on the car.
In Italy, you take a ticket when you get on and pay when you get off. It's a good system but exits are far apart because they have booths at every exit. If you miss your turn (or go the wrong way), it's a long process to get off at the next exit, pay your toll, cross the freeway, take a ticket and get back on track. I highly recommend a GPS. We survived without one but would have been much happier with one.