How much cash should I carry for driving a rental car in Italy?

My wife and I are traveling to Europe this May. We are renting a car in Florence, Italy for driving around Tuscany. We decided she will learn the language and I'll learn to drive there.

I've been trying to nail down the final preparations. I found this question covering the international driver's license. However, I've also read on the US government travel advisory website that you may need to pay traffic citations on the spot, or risk having your car impounded.

U.S. citizens driving in Italy should also note that, according to Italian regulation, if a resident of a non-European Union country (e.g., the United States) violates a traffic law, the violator must pay the fine at the time the violation occurs to the police officer issuing the ticket. If the citizen does not or cannot pay the fine at the time, Italian regulation allows the police officer to confiscate the offender’s vehicle (even if the vehicle is a rental vehicle).

What are the exact procedures for this? I'm guessing that officers in remote parts of Tuscany won't be carrying portal credit card readers with them, so I will need to carry cash. We're not planning on violating any traffic laws, but sometimes mistakes are made. How much cash should I plan on having to pay for common traffic violations (e.g. speeding, failure to yield, illegal turn in an intersection etc.)? Do parking tickets work the same way?