the tax tables only change the taxes in $50 income steps ($25 income steps if your taxable income is below $3000).
As such, adding $11 of income does nothing to the taxes due while you are in the middle of that $50 range, but as soon as you cross into the next lot....it jumps up......so it is really the tax on the whole $50 range, including $ you were not being taxed on yet.
See:
https://www.irs.gov/pub/irs-pdf/i1040tt.pdf
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*