When I rented the vehicle, I specifically asked about "Platepass" to cover tolls on my trip to Palm Springs. The agent said it would be an extra $11.99/day so that I wouldn't be surprised by any toll fines. I purchased the Platepass. Then, I received 2 bills from the 91 Express Toll Lanes, because, apparantly, the "Platepass" does not cover the 91 Express. I also received a $30 administrative fee from Dollar.
At the time of rental, the agent said that if we didn't use the pass, the cost would be refunded, but it wasn't.
Beware renters: if you purchase the pass, it does not cover all tolls. I believe you must purchase your toll pass from the California tolling authority instead.