The simple solution would be to input into a Python program and have it do the calculations instead of a spreadsheet. If you also use the decimal module then problem solved. Also, if you know there will never be more than 2 or 3 places after the decimal, then round and use a string as suggested above, but converting back to a float will yield the same result (possibly-depends on what Excel does and if the number is calculated or entered) so convert from a string to a decimal if you want to do arithmetic on it or use it as a number.
rounded = "%s" % (round(0.06000000000000005, 3))
from decimal import Decimal as dec