Counter staff will provide local information at the pickup depot. Most suppliers have e-tags in their vehicles, but you will need to check the specific terms and conditions of your rental to be sure. A popular option to pay for the use of toll roads in Australia is to either call the toll provider or arrange payment online.
Sydney: Sydney Motorways http://www.sydneymotorways.com/
Melbourne: CityLink Melbourne http://www.citylink.com.au/