Hi Red75, if it was a state law that you breached and not a federal offence (in which case the commonwealth spent conviction scheme would apply) - then if you were an adult when you were convicted of the offence and you were not convicted in a Youth Justice Court, the conviction will become spent automatically after 10 years from the date of the conviction (or, if you were sentenced to imprisonment, ten years after the period of imprisonment ends).
This is provided there was only a fine an no imprisonment longer than 6 months was imposed for the conviction.