Salik is Dubai's electronic toll collection system. There are no toll booths in Dubai providing you a continuous drive across the UAE without any interruptions.
When you cross a Salik, charges are also recorded by the rental company through the RTA Salik system. You, the car renter / driver, pays the Salik charges.
Car hire companies mark up the cost to AED 5 per salik. Here is a complete list of Salik Toll Booths in Dubai
Note: You also pay for Salik charges when your hired taxi crosses a toll in Dubai such as on Sheikh Zayed Road.