I am using the following formula to calculate my federal tax withholding
=IF(C10<1479,((C10-SUM(B13:B17)-428)*.15)+34.3,((C10-SUM(B13:B17)-1479)*.25)+191.95)
All of the other formulas I have are on the money -- SS, Medicare, Retirement -- but my Federal withholding is pennies too low. The formula is displaying 227.77 when both my paycheck and PaycheckCity show 227.83. What would cause this slight variation? Thanks.

Edit: if it's needed, B13 is a formula based on a percentage of C10, and B14 through B17 are all static.