There are 4 possibilities for a rental in Sydney/Melbourne for tolls

Either

[1] You have your own tag which you use for the rental

[2] Tolls have been included in the rental. If there is listed an item for Tolls at something like $13 a day , then Hertz will simply charge you that amount ( plus 10% GST plus, if rented from an airport, the aiport surcharge of around 27% ) as part of the rental

[3] In Sydney, You can set up an account with one of the toll companies which will then charge for the tolls plus service fee or In Melbourne, purchase day passes for the days which you use the toll roads

or if none of the above applies

[4] Hertz will charge a $16 admin fee plus charge for the tolls incurred when it receives the toll charge information a few weeks after the rental

There is no longer any risk of being hit with toll infringement fees

If you are using the Melbourne Toll roads, I would recommend getting day passes for the days which you use the roads since this will be likely be cheaper than paying Hertz. You can go to www.citylink.com.au and purchase online. You can purchase online up to 3 days after date of travel