Reply To: Table of Contents – GREP Styles

In the TABLE OF CONTENTS dialogue box in the BETWEEN YOUR ENTRY AND NUMBER box add the EN SPACE before and after the TAB
This will automatically add the space you want when the TOC os generated or updated

Make the character style with the underline style as you want it name this eg TOC Underline

Then in the TOC Paragraph Style add a GREP Style
APPLY STYLE TOC Underline
TO TEXT

This will apply your underline style to the tab only and not the en space either side of it