The voting process involved,
- Fill out ballot paper,
- Put paper in box,
- Count the papers and the result is declared.
After the result is declared what happens with the ballot papers? I could not find it on Wikipedia or the AEC website.
Here's the legislation:
In summary, (it doesn't really answer the question) the Electoral Commissioner may direct that electoral documents be destroyed if 6 months have past, and there's no continuing need for them.
Until then (the bit that would answer the question) it only says the Divisional Returning Officer for a Division (or some other Australian Electoral Officer in the case of Senate papers) "is responsible for the safe custody, in accordance with the directions of the Electoral Commissioner, of electoral documents used in the Division in connection with an election until the documents are destroyed", noting if they're used.
So we really need to ask the AEC...