wow, this is a first on technibble. Tucking in or not.
I had some techs that liked the tight tuck look and some liked the sloppy look and I didn't care as long as the work got done. The guy who liked it sloppy and not tucked in was my best employee.
I never once debated on tucking in or not. There is no need if it fits correctly.
The following is a guide to help you dress casual/professional IT. At least this is my guide.
Polo Shirt
If you are wearing a polo that fits like it is supposed to. The bottom of the shirt should just hit the top of your pockets on your pants.
The collar should not be popped :

The top most button always undone. Unless you are hairy and it doesn't fit right...
Pants
You should be wearing cargo Khakis.....not jeans not slacks.... CARGO KHAKIS, Black, blue or tan in color. No blown out knees, and no stains. The waist does not need to be at your belly button. Let them be a little loose and comfortable. Not too lose as to look like a rapper, but just a little bit. The leg cuffs should be long enough that if you sit they don't fly up to mid shin, but short enough you don't walk on them. They should cover part of your shoe laces.
Footwear
NO BOOTS
NO DRESS SHOES
Sneakers only, and if you are required steel toes, get steel toe sneakers.No Jordans!!
A casual low-cut type skate or walking shoe, black, or tan only depending on the color of your pants/polo.
Yes they do come in steel toe. PUMA even makes steel toe shoes.
If you are in a corporate office and they require a full button down monkey suit. Good luck with that.