How much tax is taken out of bonuses in Texas?

A bonus is treated like any other income from that employer...just like salary (call the money or things your employer pays or gives you anything you want - that isn't going to change what it really is and the tax authorities know that).

The percent taken out depends on all the factors you established by filing your W-4 and varies from person to person. Remember, if your just considering what percent you would have withheld to figure how much you'll have, many things are taken out of your pay that aren't income tax!