Basically, it works like this (I think):
Gross * 52 - Standard Deduction ($6300, 2015 single) = Taxable Income * Tax Rate (Varies depending on taxable income. we'll use 15%) / 52
So, using my previous example,
$400 * 52 - $6300 = $14,500 * 0.15 / 52 = $41.83
$400 + $150 (10 * 1.5 * 10) * 52 - $6300 = $22,300 * 0.15 / 52 = $64.33
Note that this is federal only (state, ssi, etc change it more) and that such an increase would also yield a higher tax bracket, which is what most people have a problem with. Now, at the end of the year, their actual annual earnings are calculated and taxes applied appropriately. Any excess is returned to them. So at paycheck-level, it seems like you're getting hit hard but it evens out once the actual earnings are calculated.
Personally, I just avoid overtime because it cuts into my midget porn time.