In HS rules do I grant time if a team does not have any left or do I ignore the request.

By rule yes. But, consider this. dead ball; coach, "time out", Official, "you are out of time outs, do you still want it". Most of these cases are just reactions. Player in trouble and calls TO, and you blow the whistle. So, yes in HS and college the TO is granted.

A team can buy an additional time out if they have used up all of theirs. Award the time out and access the team with a technical foul.