Travel guides all seem to differ in their opinions on when to tip and when not to tip in Australia, and rightly so, it's a complicated matter. Australian service industry workers are paid better than their American counterparts, so they aren't relying on tips to pay their bills, however if you went to a city restaurant, enjoyed excellent service from a friendly waiter, thought the food was wonderful, gave a $100 note to cover a $96 bill and then asked for change, you'd be committing a serious cultural sin. At the same time, if you ordered a meat pie from a roadside café in a rural town and gave a large tip, you'd probably get a few sideways glances (unless you had an American accent, in which case they'd be more than happy to take advantage of your generosity).
The best rule to follow is that it's polite to tip someone if they've given you good service, you've spent at least a few minutes using the service and you're paying money for the service. 10% is about the right amount, although you can get away with 5% or 15%, depending on whether you think it's worth it. Definitely tip in a restaurant, but you don't have to tip someone you're not giving money to (such as a hotel concierge who's given you directions)
Most people will tip in a restaurant. Waiters expect at least about 5% if there's been nothing really wrong with the service or food, but 10% is much more appreciated. If you didn't like the service then feel free not to tip - it is by no means compulsory. You don't need to tip in fast food restaurants.
If you're buying a round of beers over the counter at a bar, you don't really need to tip, but don't get picky over the change either - if the drinks cost $19, give them $20 and say 'keep the change'. You'll get a smile and if the bar is busy you'll probably get served a little quicker next time.
Room service staff and concierges don't really expect to get a tip for doing their job - they're getting paid by the hour and although they won't turn a tip down, they're not going to think you're evil if you don't.
Some people do, some people don't. It's polite to at least round up the fare to the nearest dollar or so. Feel free to reward good service, or vice-versa. You don't really need to tip airport shuttle drivers, limousine drivers appreciate the change.
Delivery people (such as pizza boys and the like) get paid per delivery, and if they're lucky they'll also get an hourly wage similar to a Mongolian toilet cleaner. Take pity on them and tip something.
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