I too work for the Gubment and I am a bit of a higher up person - so I wear a tie about 90% of the time - no manditory, but I LOVE ties - no choice when wearing a tie IMO. BUT, aside from button down collar shirt tucked into slacks - I NEVER tuck.
NEVER tuck a tee shirt.
NEVER tuck into jeans.
NEVER UNDER ANY CIRCUMSTANCES TUCK ANYTHING INTO SHORTS!!! IMO, the worst is polo tucked into shorts with leather braided belt and topsiders sans socks - I will kick you in the baby-maker if you do the shorts tuck.