TL;DR: 1/10 has an infinite repeating binary expansion. (think 1/3 in decimal - 0.3333333) The part that really gets you into trouble is that the repeating pattern is 0011, which means it rounds differently depending on how many digits of precision you give it.
Can we use WolframAlpha to show why 0.1 cannot be represented as a floating binary?
And why floating numbers shouldn't be used for currency operations.