There is only one file type that uses the .TAX2016 extension:
TurboTax 2016 Tax Return
A TAX2016 file is a United States tax return created with the 2016 version of Intuit TurboTax. It contains a user's personal information and federal IRS tax forms. It may also include one or more state forms for the 2016 tax year. TAX2016 files may be encrypted if saved with password protection since they store sensitive personal and financial data.
Updated: December 7, 2017