When the declared amount is greater than AUD 1000 ( about USD 638), tariffs begin to be levied.
The total tariff in Australia consists of the following four parts:
a). Import DECN10 Air charge: AUD 40.20 (about USD 25.65) / per entry (fixed charge)
b). AQIS — Entry charge Air: AUD 15 (about USD 9.57) / per entry (fixed charge)
c). Import tariff = FOB price * tax rate
d). GST = (FOB price + freight + import tariff) * 10%
Total tariff = DECN10 + AQIS + import tariff + GST
FEDEX handling fee = total tariff * 2% (minimum charge AUD 6 (about USD3.83), maximum charge AUD 299 (about USD 190.8)).

For example: 1000 large car flags sent to Australia, the declared amount is USD 1200, the freight is USD 900,
Import tariff = USD 1200 * 5% = USD 60
GST = (USD 1200 + USD 900 + USD 60) *10% = USD 216
Total tariff = AUD 40.2 (about USD 25.65) + AUD 15 (about USD 9.57) + USD 60 + USD 216 = USD 319.3
If arranged by FedEx, there will be a handling fee = USD 316.78 *2% = USD 6.33, total cost: USD 316.78 + USD 6.33 = USD 323.11
If shipped by DHL, the handling fee for paying the tariff is RMB200 (about USD 31) / package.
Apart from that, if the declared value is less than AUD 1,000 (FOB price), the consignee will be free of duty and tax.
Regarding the import HS code and the tariff rate, you can obtain the information via the website: http://www.customs.gov.au/tariff/tariff2012.asp.

Note: The amount will slightly fluctuate based on the exchange rate.