For most people you should be looking at saving 20%-34% for taxes at the end of the year. Now after deductions you may pay less but unless you're homeless, native american or a convict you're probably not going below 20% being owed. Also note that you can't even use deductions if someone claims you as a dependent, unless you want them to get in trouble you may have to tell them that they can't claim you.
Also to note. You'll probably have to PAY someone or for a program to file your taxes also. Expect $60-$200 for that also depending on how complicated they get.