Maybe rounding error isn't the best term, but it seems below the threshold to worry about. Here in California, probably at least 30K of it would go to taxes anyway, and I wouldn't know how much within $2000 of accuracy unless I paid a tax accountant $300 to type the numbers into their software. Notably, the IRS requires you to be within 90% of your tax liability over the year to avoid penalties. 0.1*30k is $3000, so the IRS seemingly agrees that $2000 on $100K is below the threshold of being substantial.