How can I know if I have to pay road tolls between Los Angeles and San Francisco?

Nowadays, nearly all rental companies offer you the option to handle that for you (for a fee, of course).

By using the road, you took the option.

There are minor differences, but for reference here the National Car Rental rules (forgive me if I am 5 cents off):

1. You pay all the tolls that are to pay, for the normal price.
2. Each calendar day you used a toll road, you pay a convenience fee of 4.95 $
3. The maximum of all convenience fees will not be more than 19.95 $

So if you for example used Toll Roads on three days, you pay the toll itself, plus 3 * 4.95 $.

They will deduct it automatically from the credit card you used to pay the car, and it will be a while (because the Toll road authorities take their time). My experience is between 10 and 40 days.

Either way, there is nothing you need to do. Just accept the charge when it comes on your credit card.

With a rental car, you'd hear from the rental car company eventually if you skipped out on any tolls, usually with a large added fee attached. They'll just bill your credit card.

However, unless you drove down any express lanes, which are toll/carpool lanes that look like this, with big signs showing a price and restrictions, there are no "hidden" tolls along your route.

I am assuming you didn't drive on any of the toll roads in Orange County, which is south of Los Angeles. You can check out a map of those if you were in that area.