Google Calculator Fun/Bug?

I realized tonight that Google Calculator will give you incorrect results. http://www.google.com/search?q=10000.01+%2B+10000.03999999999999 ...gives me 20000.1 https://www.google.com/search?q=10000.67+%2B+10000.02 ... gives me 20000.7 I wonder why it insists on rounding my answers (and sometimes incorrectly)? Any hypotheses? Is it a bug? Do they only allow a certain number of significant figures?