I agree with @dpark on this: casual shirts tucked in do not look any nicer.

If it's a casual, soft wash shirt, it looks fine untucked. If it's a dress shirt, it doesn't. I think the line between casual shirt and dress shirt is pretty defined, but I'm sure others disagree. Even websites like J Crew and BR separate the shirts out this way. Tucking in a casual shirt is like tucking in a t-shirt to me; it seems pointless. If I was trying to dress nice enough to tuck my shirt in, I would be wearing a nicer shirt.

I dislike untucked shirts with blazers. I also dislike casual shirts with blazers. If you're taking the extra step to wear a blazer, wear a tucked in dress shirt to complete the look.