Visiting The Usa With Spent Convictions?

I know you legally have to declare all convictions but all of mine are classed as spent/sealed (Australia). None are drug or serious damage to property or person like it asks on the ESTA questions. I am under the impression that under US law I need to tell them but under Australian law the government can't tell the US government because they are spent. From what I know it can only appear on a background check when applying for an Australian visa, working with children, elderly, police, military, and anything to do with firearms or security. So unless I snitch on myself they'd have zero way of knowing.

If I want to go on a holiday I may as well just not declare it if they have no way of originally knowing, is this right?