Pleased to see this crop up in TalkMail, as it was my most recent travel hassle. I'm surprised by how much variation there is in practices across companies. I was in DFW for a wedding a couple weekends ago, and rented from Thrifty/Dollar.
Their policy/hard sell was: $15 plus toll per toll (service fee for matching the toll to me, you see), OR I could sign up for their program for $13/day (for each day of the rental) including tolls. They were uninterested in helping me mange my routing: "Where are the tolls?" "They're everywhere." "How much are the tolls?" "Variable." "Do you have a map?" "They're not on our maps. You'd need to rent a GPS." "This sounds like a scam." "It's our policy."
At the wedding, friends had rented from different companies. A couple said nothing, a couple were explicit that toll amounts would be passed onto the renter's credit card. One may have had a modest daily fee.
Are there regional or national policies that different companies have? I don't think there was good way for me to know this hidden markup on the car I reserved when I reserved it. (Though next time I'm walking to the next counter…)