The problem you are having is that ACA uses the raw number, not the formatted/rounded number, when calculating the total of a Column in a Schedule Table, and then applies the format to that number. Sometimes you get lucky, and the final number is the sum of the listed, rounded values; sometimes you do not get lucky and there is a variance.
There is a way around this. Instead of scheduling the automatic Area property directly, you can set up a Formula property that either does the rounding (if you cannot achieve your desired rounding with a Property Data Format) or that passes through the rounded value. In the latter case, you will want to have a Property Data Format that does the rounding, but does not add any text to the result (like " SF" or " m2"). You can apply the "area" formatting, with text, to the Formula property, to get the " SF" or " m2" suffix in the Schedule Table.
This blog article discusses using a formula property to get ACA to use the rounded value in the Schedule Table. The example in the blog article was geared toward getting a Schedule Table with a Quantity Column to treat identical rounded values as the same, even when the source values were slightly different. The same techniques will work to make ACA use the rounded value when calculating the sum of a Column.
I will try to find time to put together a sample file that illustrates the two techniques and post it here.
