Swyftx has taken a unique approach to handling Fiat currencies deposited on the platform, with the intention for this approach to minimise costs and trade fees for it's users. This is done by operating all trades on the back-end using USD.
All AUD deposited to Swyftx will be converted to a USD equivalent balance using the AUD/USD indicative rate show on the AUD deposit screen. The platform allows toggling of the base trading asset between USD and BTC with more fiat and crypto bases to be added soon (including ETH and AUD). This gives users the added flexibility to trade their account balance on the most liquid pairs in Satoshis (a common practice) or USD (global market prices) regardless.
Remember global market prices of just about anything are dictated by the largest volumes and biggest economies - in the case of Digital Currencies this is USD.