Excel round function not adding to zero

I have a worksheet with about 8000 rows of data which need to sum to zero (this is a journal that needs to be zero for posting into our ledger). The ledger requires that all numbers be formatted to two decimal places.

The issue arises in that I have rounded all the numbers to two decimal places (using the round function), however when I sum the column the value does not equal zero. It comes to something like 0.0000045698.

I have checked that all the entries are rounded to two decimal places in various ways and they definitely all are.

I have also noticed that there are a couple of large negative numbers and if I remove these, the sum cell shows two decimal places as expected.

By way of additional info, if I round to more than 2 decimal places, I get exactly the same number in the sum cell, whereas if I round to 1 decimal place I get a different number (which is not zero). If I round to zero demical places, I get an integer as I would expect.

I have looked at some forums and guess that this must be to do with the way Excel stores numbers, particularly negatives, but I can't see a solution.

Any thoughts?

Thanks