I have several formulas that are contributing to a final price for an item.
The result of last formula is that 2 x $610.60 = $1,220.21, and I can't find
the error. There is one related cell that uses the ROUND function, and I
wonder if that is contributing to the error. The contents of the related
cells a

=ROUND(IF(M880,K88*(1+M88),0),2)+N88

where M88 is a percentage mark-up (11.0% formatted as a percentage with 2
decimal points.)
where K88 is =SUM(I88:J88) - I88 and J88 are both numeric values
where N88 is a numeric value

I have a feeling that somewhere in one of my formulas there is a number
that's reading many more decimals that two, therefore 610.60 x 2 is larger
than 1,220.20. I checked all cells, and none have more than 2 decimals.

Any ideas where I'm getting the extra penny from?