Depending on what browser you are using changes what happens. Some browsers may round the value. Some force it to round up (math.ceil in some langauges) and some round down or "truncate". For example, Google Chrome truncates the decimals.
You can easily test the effects of this by print screening and then later checking the size in a paint editor (paint, paint.net, adobe photoshop, etc.)
Very interesting question, however :)
