When calculating FX profit/loss, do I convert the received currency amount to JPY?

I'm trying to calculate profit/loss on an FX transaction for tax purposes.

For example, if I convert 9,000 AUD to 6,418 USD at Prestia, do I use the USD->JPY rate as the "final amount"? or do I use the AUD->JPY rate as the final amount?

It makes more sense to use the USD amount since that's the actual amount received.

Thank you.