Feel free to undo the top button of your shirt and leave your tie just tight enough to keep the collar in place. You can also leave the skinny part of the tie that is usually kept hidden behind the front of the tie out to hang loosely. However, this method isn’t easy to pull off as it can turn sloppy easily.
The end of your tie, no matter how it's tied, should always hang down to the middle of your belt buckle. This is a sort of golden rule that applies to how to wear a tie regardless of the dress code.