What I would suggest is to talk to a local professional accountant or your local tax office about this. The reason behind this is because the tax laws are different in every country and even regions within countries. I'm not 100% sure if the tax laws in Australia would require you to charge taxes on shipping rates. For example, you do need to charge taxes for shipping rates within the USA but you might not for another country. Shopify has a help document which talks about it a little more here.
I did some digging and did find some information on when to charge GST when selling from Australia, but couldn't find anything specific on taxes for shipping rates. I can't stress enough to visit a professional to double check on this and any other tax questions you might have.