How is the "fully stocked" reward for a level calculated?

I've noticed that when I fully stock a level I receive a small amount of coins. Since I've seen the amount vary a lot, even when stocking the same level, I was wondering if there's a formula behind it or if it's chosen randomly every time.

After testing this theory a few times on different floors, I was able to determine that the bonus = ~ 4.98% * [total amount of all 3 items in stock at the time of being fully stocked]

1st full stocking item:

41 bonus / 823 total in stock= .0498...

2nd full stock bonus:

22 bonus / 441 total in stock = .04988.....

3rd full stock bonus:

124 bonus / 2489 total in stock = .0498....

These were different types of floors at different heights.

The bonus is total stock on the floor divided by 20 (i.e., 5%) - rounded down. The rounding would account for the difference between the 5% and the 4.98% quoted above.