Small but significant point: the record of the offence or the fact that you have been dealt with by the court is never expunged.
The "spent conviction" provisions allow you to tell a statutory lie. That is, you are authorised by law to deny that you were dealt with by the court in relation to a matter that satisfies the defintion of a "spent conviction". (See for instance section 85ZV of the Commonwealth Crimes Act 1914.) There are also restrictions on the disclosure by and the use to which the record may be put by the record holder.
But the record will always be there.