I just did a quick dummy booking through the Qantas site to check the tax figure.

According to it, the tax for a Syd-Bkk return ticket should be $210.88


I then compared that with the tax figure shown on a similar booking on Zuji with a different airline (emirates) and the tax was $212.28

And then finally I checked a similar Qantas booking on zuji for the taxes. The figure was $210.88

Sorry, but I think the calculation is correct.