As an Australian developer, any sales to Australian customers include 10% GST (Goods and Services Tax).

Apple send a monthly GST report containing the amount of tax we need to pay for our Australian sales, which makes reporting super-easy.

Side note: Apple don't charge the tax on top of the price, so earning a 99c sale from a US customer (net revenue ~$0.70) is far more valuable than a 99c sale from an Australian customer ($0.63)