If you’re planning a business trip or vacation, you may have to make a decision about how to pay tolls when you rent a car. Most rental car companies offer ways to pay tolls automatically, but that convenience comes at a cost. Here’s how the devices work. In many parts of the country, your rental car comes with a transponder — a small electronic device on the windshield. Once set to ON or OPEN, tollbooths or scanners automatically scan and charge...