This table can be a little confusing without further explanation. Note that everyone is taxed in steps. A single, non-head of household person earning $100,000 is not taxed 28% on the entire amount. Instead, he is taxed 10% on the first $8,500 earned, 15% for the portion up to $34,500, 25% for the portion up to $83,600, and 28% for the remainder.
This clarification is important to quell some misleading rumors. It has been suggested that if an employee earning $8,500 (take home after taxes: $7,650) is offered a $5 pay raise (enough to boost him into the next tax bracket), it will actually decrease the total amount he takes home (suggested take home after taxes: $7,229.25). But this is incorrect. Only the $5 above $8,500 will be taxed the higher 15%. In this case, his ACTUAL after taxes take home would be $7,654.25.
To learn more about the U.S.'s federal tax system, check out the Progressive Tax definition.