[Cryptography] Throwing dice for "random" numbers

[Dave Horsfall]

I know that I should know the answer to this, but for some reason my brain 
appears to be in neutral (call it early senility, as I turn 66 soon).

I picked up a a pack of 12 dice from one of those discount stores for the 
princely sum of AU$2 (so we can safely assume that they are not exactly 
casino-quality[*], but at least the pattern of dots is correct).

So, the obvious question is: how unpredictable (not "random") would their 
sum be, modulo N, given that each individual source is numbered 1-6?  I 
know that I can just throw a decahedronal die for example, but the 
shipping cost to here down-under seems to outweigh their value, and there 
does not appear to be a gaming shop within coo-ee of where I live.

It's not for any particular application, but merely an exercise, and as I 
said the mathematical part of my brain seems to have gone on strike...

Thanks.

[*]
I vaguely recall an experiment mentioned in a thread (likely started by 
me) that showed that a "toy" die tended to land 6-up slightly more than 
expected because of the small shift in the centre of gravity, due to the 
6-side dimples removing more mass.

-- Dave