The amount of taxes withheld depend on the pay period (weekly, monthly etc.) and what you put on your W4---such as single or married, and the number of exemptions.
If you can give me this information for your paycheck, I can give you approximate withholding amounts.
Your employer has a couple of options regarding how to withhold for a bonus, or supplemental, check. He could use your W4 guidelines and treat it as a regular paycheck, or he could use bonus amount, which is 25% federal withholding. Most employers use this method for convenience.
Assuming a 5000 check, computed as an annual bonus (and you have not exceeded 97.5K in salary this year):
Annual Gross Pay