floating point representation is approximate only as you cannot have precise representation of real, non-rational numbers on a computer.
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when operating on floats, errros will in general accumulate.
however, there are some reals which can be represented exactly on a digital computer using it's native datatype for this purpose (*), 0.5 being one of them.
(*) meaning the format the floating point processing unit of the cpu operates on (standardized in ieee754). specialized libraries can represent integer and rational numbers exactly beyond the limits of the processor's internal formats. rounding errors may still occur when converting into a human-readable decimal expansion and the alternative also does not extend to irrational numbers (e.g. sqrt(3)). and, of course, these libraries comes at the cost of less speed.