https://github.com/bitcoin/bitcoin/pull/79
This modifies FormatMoney to display full-precision values (with trailing zeroes trimmed correctly-- e.g. 0 is 0.00 but 0.00010000 displays as 0.0001).
And ParseMoney allows entry of full-precision values.
And JSON's AmountFromValue doesn't round to two places, so you can send/move full-precision values.
I haven't tested this with the GUI bitcoin yet, it will probably require UI layout tweaks.