Heya,
Many things to consider:
- Your residency. You might still be an Australian resident for tax purposes (from what I read, good chances are that you are), so you have to take this into account.
I'm not sure about the rule for the US, but pretty certain that, even if you don't pay anything in the US, you would pay something here.
- Most tax treaties mean that you would have some tax withdrawn from the US. Again, double check.
Question: Why would you sell? Why don't you transfer to Interactive Brokers and take back the funds only when/if you need them?