There is only one file type that uses the .TAC extension:
ActiCalc Data File
File created by ActiCalc, an advanced desktop calculator for Windows 98, 2000, and XP; saves a visual tape that stores a history of calculations; allows the history to be updated and imported into Microsoft Excel spreadsheets.
NOTE: ActiCalc is not supported on Windows Vista or later. The software has been discontinued.
Updated: February 25, 2013