The shipping and insurance costs will have to be included in the total for the calculation of GST Whereas the Duty is calculated on the Au$ value, the GST is on the total of the Au$ value plus Duty plus freight/postage and insurance costs.
Each also atttract 10% GST.
You may also incur an additional $52 Customs Entry processing charge.
Postal items:
If the value is under $1000 and the amount of duty and/or GST is under $50, the duty/GST is waived.
If the value is under $1000 and the duty/GST comes to $50 or more, it is payable.
If the value is $1000 or more, the goods must be cleared on a Customs Entry for which there is a $52 processing charge and the duty/GST is payable no matter whether it comes to more or less than $50.
Freighted/couriered items:
If the value is under $250 and the amount of duty/GST is under $50, it is waived.
If the value is under $250 and the duty/GST comes to $50 or more, then it is payable.
Again, if the value is $250 or more a Customs Entry must be lodged ($52 processing charge payable) and the duty/GST is payable no matter whether it's more or less than $50.
But note that courier companies (such as FedEx, DHL, UPS) automatically lodge Entries no matter what the value, so you'll definitely incur the $52 charge on every shipment whether duty/GST is payable or not.
So it depends on which scenario your order fits.
Be aware that if you have several packages arriving at once, they will be treated as one shipment and added together.