If a broad-ish and bounty-worth question gets many equivalently good answers (i.e. imagine a reference request where user A gives 2 good references and user B gives other 2 good and different references), how to assign the bounty? Can it be divided among the answers?
(My current bounty awarding algorithm in these cases is to give it to the user with lowest reputation)
No, bounties cannot be divided. From a post on MSE:
Can I affect / divide part of my bounty to two (or more) users?
No. If multiple answers to a single question have earned bounties, it's because the question has been subject to multiple bounties.
However, as alluded to in the quote, it would be possible to place a another bounty on the same question. (Note though that the size of the bounty would need to be doubled, if it was not maximal.)
I think your current decision-process is fine. Generally, I think one should not overthink this, but just award it as one finds it appropriate in the moment, possibly explaining the rationale.
