Australian GST (goods and services tax)

[RodG]

One simple option may be to set all your taxes to zero, and have the same price for Australia and OS. This mean it's always correct for Australia, and you can always compensate OS purchases with cheaper shipping rates or other bonusses. it's not ideal, but it keeps things simple...

We don't get this option. If we are registered for GST then it is assumed everything we sell/buy/provide has a GST component attached to it (regardless of whether credits for it are claimed or not, unless of course, it is an exempt item). No sensible merchant would bare the GST costs when they have the chance to pass it on.
If we are not registered for GST then we aren't allowed to charge GST anyway so it is a moot point...

Cheers
Rod