Most goods in Australia are subject to a 10% GST (goods & services tax). This includes things bought in shops as well as dining out. The only exemptions are fresh food such as milk, bread etc. All prices listed include tax (occasionally with the exception of plane tickets), so you should never have to pay more than the advertised price.

 The government runs a scheme called the Tourist Refund Scheme whereby you can claim a refund of the goods and services tax (GST) and wine equalisation tax (WET) that you pay on goods you buy in Australia.

To claim the refund you must buy goods totalling $300 (GST inclusive) or more, bought from the same store, no more than 60 days before you leave Australia. You may purchase several lower-priced items from the one store, either at the one time or over several occasions within the 60-day period, provided the total purchase amounts to $300 (GST inclusive) or more. You may buy goods from several stores, provided each store's tax invoice totals at least $300 (GST inclusive).

The goods must be in your hand luggage as you leave. Customs no longer stamps your receipts before you enter so that you can check your bags through, you must carry it on the plane with you.   If you have a receipt for MORE THAN $1000, you need to have the store enter your name and address on the receipt, otherwise it will be rejected.   The scheme does not apply to goods you consume while in Australia but does allow you to use goods such as cameras etc before leaving the country.

Further details can be found at: Australian Customs