Thank you for the response to the question I asked yesterday (regarding rounding up from $2.273).
I wanted to just clarify regarding the nature of the money that I am holding: the store returned the group’s money to me and I need to now return the money to the group, so I am like a middleman between the store and the group. Is the money that I am holding considered a loan from the group to which ribbis would apply?
Although you were doing what they wanted you to do, however the money was given to you, and you could have used it for your own personal use and give the group other money. (Which is most probably what you did, because the store didn’t give you such small change). Therefore, it is considered a loan regarding ribbis.