hint (from my bugs)
see MSDN Math.Round( decimal d, int decimals ), which I use
MtGox rounds numbers NOT SAME:
If the value of the first digit in d to the right of the decimals decimal position is 5, the digit in the decimals position is rounded up if it is odd, or left unchanged if it is even. If the precision of d is less than decimals, d is returned unchanged. The behavior of this method follows IEEE Standard 754, section 4. This kind of rounding is sometimes called rounding to nearest, or banker's rounding. It minimizes rounding errors that result from consistently rounding a midpoint value in a single direction.

some datas:
{"channel":"24e67e0d-1cad-4cc0-9e7a-f8523ef460fe","depth":{"price":30.22425,"type":1,"volume":1},"op":"private","origin":"broadcast","private":"depth"}
{"channel":"d5f06780-30a8-4a48-a2f8-7ed181b4a13f","op":"private","origin":"broadcast","private":"ticker","ticker":{"buy":30,"high":31.89,"last":30,"low":18.6,"sell":30.2243,"vol":98781}}