The commission rate remains the same regardless of how you trade - so if you transact 20,000 in new volume, you would be charged proportional to that new volume.

 E.G. if the commission rate is 4.5 AUD per lot, and you trade 20,000 AUDUSD - your commission would be 0.45 AUD per side of the trade, or 0.90 AUD round-turn to open and close that position.