If they rental agency is paying those taxes then they are aware of them, have them entered into their CRM, and can inform you anytime by pulling a simple DB query. There is no excuse in 2020 to not know exactly what the price is and keep that from your customers.

I deal with reputable rental companies. The rental price is based on demand but everything else is a known quantity. I’ve never had the quote priced higher than the online quote. And in a few cases I’ve had it go down by using certain credit cards or loyalty programs.