The gear I showed in this thread
http://www.talkphotography.co.uk/forums/showthread.php?t=94224 has a 20mm macro lens on it although I've also got a 50mm for lower magnification/longer working distance usage.
As first stated, the 105 will work fine but the 50 will give you a much larger magnification.....either way, you'll doubtless be needing to get some light in there somehow.
Bob