There is only one file type that uses the .TAX09 extension:
TurboTax 2009 Tax Return File
Tax return created by TurboTax 2009, a U.S. tax preparation and filing tool; contains 2009 tax forms and tax data entered by the user; used for filing taxes during the 2010 calendar year for the 2009 tax year.
TAX09 files are much more commonly seen with the .TAX2009 extension.
Updated: May 15, 2010