Formula for exact penny increments, eliminate Excel's precision variances

I've been searching the net for the last hour to find an answer to this but I can't.

Sorry if I'm asking a stupid question but this is killing me.

I'm building a pretty big matrix in excel 2007 and I need to copy down -100 +.01 to create a table that goes from -100, -99.99, -99.98....through to +100.00.

So I simply put in a formula.... but when I copy the formula down about 10 numbers down or at irregular intervals the equation fails and turns, say 99.9 into 99.899999999. I need it to be exactly 99.9 as it is used in a IF formula.

Does anyone know how to stop this happening ??

Put -100 in A1.

Put this formula in A2, then copy A2 down as far as needed:

=ROUND(A1+0.01,2)