There is only one file type that uses the .TAX2010 extension:
TurboTax 2010 Tax Return
Electronic tax return document created by TurboTax 2010, a United States tax preparation and filing application; contains 2010 tax forms and data entered by the user; can be validated and e-filed using the software once the tax data is complete.
NOTE: TAX2010 files store Federal and State tax return information for the 2010 tax year. Therefore, they are most commonly created during the 2011 calendar year.
Updated: February 4, 2011