Everybody in service industries are paid well compared to the US.
So tip waitstaff and bartenders only for exceptional service or friendliness or just leave the change.
Most such places will have a tip jar that will be divided between the staff you interact with and the staff you don't - like out in the kitchen washing the dishes.
I tip people/places that made me feel good when they didn't have to and when I'm a bit cashed up and especially when I'm a regular customer.
It's never bad not to tip. We know not everybody has extra money for tipping and we know we're all paid pretty well compared to other people. Some of us will even ask you to offer your tip instead to a charity collection box we might have on the counter!
The kinds of places that would insist on tips are the kinds of places that add an equivalent charge on the bill. Don't tip at places that do this - you would be tipping twice.
A taxi driver would have to absolutely amaze me to make me want to tip. Sadly it's much more common for a taxi driver to be shoddy or even scam you a little bit, such as taking a longer route than necessary.
Personally, I like the taxi drivers who have obviously just immigrated from another country. Sometimes their English is not great but they often go out of their way as Aussie drivers seldom would, and they will get a hard time from racist Aussie passengers. It's a business where people get jaded very quickly. Only encourage the good ones.
But never tip a taxi driver who acts like they're expecting a tip, especially after hearing a North American accent. I would put this in the "scam" category.
Overall I would say the most common tipping practice in Australia would be to attractive young bartenders! They're the only ones who will really make noticeable extra income from it. And they're the ones most likely to receive tips from people who say they never tip (-: