That’s the extension for tiff files. There’s prob tons of commercial products to do that if you google.
If you’re not afraid of the command line, use ImageMagick. The
instructions are fairly simple.
If you’re more of a GUI guy, use
XnView (freeware). It’s an image browser, but it has excellent conversion utilities bundled. Open the browser, then select all the images (ctrl-A usually), right click, select 'batch processing' and for format pick jpg and click on options to adjust the quality settings to your liking.
For more info read the wikipedia entry on
TIFF