If you elect to receive the rental agreement via email, it contains a link to both the full rental agreement as well as the rental jacket with the return form. I just clicked on the link from an email I received from a rental yesterday and this was on page 4 of 7 of the linked rental agreement PDF:
IMPORTANT INFORMATION REGARDING TOLLS
You are responsible to pay all tolls. For your convenience, we offer
PlatePass, an electronic toll payment system operated by PlatePass
LLC, for use on toll roads in the areas specified below.
************
In the following areas all our vehicles (even without a windshield toll
transponder) may use any cashless electronic toll lane: The entire States
of FLORIDA, GEORGIA, COLORADO, NORTH CAROLINA, and TEXAS, and in Seattle,
the TACOMA NARROWS BRIDGE and the SR 520 BRIDGE.
TO USE PLATEPASS IN THESE AREAS, pass through a cashless
toll lane. You will be billed automatically as outlined below.
IF YOU DO NOT WISH TO USE PLATEPASS IN THESE AREAS,
use only traditional cash toll lanes (if available) and make payment
directly to the toll authority. If your rental vehicle includes a
transponder, make sure it remains fully closed within the shield box.
In both video and transponder toll areas, pay all tolls with cash or your
own toll transponder (where permitted) compatible to the toll road.
Some toll roads no longer accept cash payments. If you incur a toll
on these roads, without using your own compatible transponder, you
will be enrolled in PlatePass.
***
The rental jacket was also linked to the email which you can
view here. It also contains the info on PlatePass. You can try to say you didn't know or didn't receive it, or something along those lines, but I'd guess that going to be an uphill battle as it's disclosed all over the place based on what I can see.