IRS in their infinite wisdom uses the tax tables and NOT the tax rate schedule. 

going from ....199 to ...200 moves from the ...150 to ...199 tax to the ...200 to ...249 tax. So a change of even $1 can cause extra tax on $50.

See page 73 https://www.irs.gov/pub/irs-pdf/i1040gi.pdf 

Tax is what you pay the big bucks for. PTO is correct