Hi charterbooks,
At this time, automatic discount terms and/or price levels are a feature only available in some QuickBooks US products. While it is not featured in QuickBooks Online Australia, you would need to add the discount manually when recording the invoice, bill or so on.
I would be more than happy to pass this on as a product enhancement insight to be considered in a future update and would also encourage you to submit your feedback in-product by accessing your Settings > Feedback. All feedback is considered as we are constantly working towards improving your experience using QuickBooks Online. I also encourage you to visit our QuickBooks blog which will keep you updated with new features and updates.
-Kass
