If you found money laying between the collection boxes, if it was between the nidava and the shikalim and it was closer to one of them, it goes to that box. If it is half way between the two, it becomes a nidava.

The same is true between the boxes for wood and frankinsence, if it is halfway it goes to frankincense.

The same is true between the boxes for kinim and olas, if it is halfway it goes to the olah box.

The same is true between the boxes for maaser sheni and chulin, if it is halfway it becomes maaser sheni.

Shikalim 7:2

Money found in front of the animal sellers in the Bais Hamikdash, is considered maaser sheni. In Yerushalayim during yom tov, the money is maaser sheni, but during the year it is chulin.