Right now the precision of each payout is randomized as well. If course, if there are only 2 or 3 payouts (which there are if amounts are small, due to tx fees), then most of them will always have the same precision, because the sum of them must still add up to the amount the user wants to withdraw.
Charge a random fee? Something between 1.5% and 2.5%? Even 1.95-2.05 would probably help.
It would be interesting to implement the distribution you have provided instead of blind randomizing. However, I don't see that it does much for anonymization, since the fact that the money came from our service will be visible anyways (as of now, all payouts are mostly done from the same address), and analysis of precision does not do much for identifying the deposit associated with this withdrawal, since they all are randomized. Or am I missing something?
Why would you do this? You move all funds to one address?
Of course that helps identify where the money comes from. Now you know it comes from some of your 1, 10, 100 customers. You'll never have so much traffic that that fact is useless.
Are you doing this because you are paying your own coins until you build up a new large stash of deposited coins? Like seed money that happened to be in one address? Seems you could have mixed that up some itself.