As others have already pointed out, you are running into floating-point errors. There are a number of solutions you might want to try:

• Use only integer values i.e. use cents/pennies/bah instead of dollars/pounds/foo (already mentioned previously)
• The use of a module such as Math::BigInt might help here?
• Could potentially round the values, using sprintf and doing a string comparison - this may suffer from the same issue as you are already seeing.
• There may be arbitrary precision Math modules already out there? Anyone?

If this is a financial application, then the use of integer values, if possible, should be the way to go.