that is a general problem in computing (see [Wikipedia on Floating Point Values][1]). the computer cannot 'really' display a 0.7, instead he saves that the number as something like 0.666879345.
Therefore I don't think what you want is possible and a problem of the represantation of floating values in general.
[1]: http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems
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