Trading in Digital Currency itself is not subject to GST from 1 July 2017.
This means that you do not charge GST on your sales of Digital Currency and similarly, you are not entitled to GST credits for purchases of Digital Currency.
You do not have any GST consequences in relation to buying or selling Digital Currency, or using it as a payment, if you are not carrying on a business.
If you are carrying on a business in relation to Digital Currency, or as part of your existing business, or if you are accepting Digital Currency as a payment in your business, you need to consider any GST consequences that may arise.
Source: ATO Website - GST and digital currency