Unless your using an overseas broker then you will need to register your company and be liable for the company tax rate.
"To trade in Australia, a foreign company (Foreign Company) must be registered under Part 5B.2 of the Corporations Act 2001 (Cth)(Act). Section 601CD of the Act provides that a Foreign Company may carry on business in Australia if it is registered under Division 2 of Part 5B.2 of the Act."
