Related על כתובות 196:1

[If] five said to one, "Go and bring us ten loaves of bread" [or] "[Go and bring us] ten bunches of vegetables," [and] he brings each one to his face (i.e., he brings that person what was purchased with that person's money), [then the] chaverim that are among them (i.e., among the purchasers) do not need to tithe except for their own portions. [But if] he brings them mixed together [so that he cannot tell which produce was purchased with which money], [then] the chaverim that are among them need to tithe on everything. If they gave him one in addition (i.e., the seller delivered one more item than was ordered, e.g., a baker's dozen), Rabbi Yehudah says, "It belongs to the messenger," and Rabbi Yosei says, "It is in the middle," (i.e., they all divide it, see Y. Dem. VI.8.6 ["רִבִּי יוֹסֵי אוֹמֵר שֶׁל שְׁנֵיהֶן"]).