My husband and I are not married legally but married by traditional ceremony.

No marriage lisensce.

Should we still file as 'married'? Because I'm not sure if we need a marriage license to do that, but we been together married for 7 years. I don't want to get audited by the IRS and they will ask for a license.

Where do you live? Some states recognize common law marriages as legal.

Otherwise, you are not married. Go get a license for furture use (Las Vegas is a good place to get this done) and hope you do not get audited for the past 7 years.