I believe this has to do with occasions where due to 'rounding errors' and the sum of the details may differ from the total amount by a penny or two, a rounding G/L account is available to post to. This often heppens with MultiCurrency where exchange rate conversions are involved.

This would be similar to the rounding account one might see in A/R control account sets when multicurrency is enabled.

There may be a more clear answer that another may wish to provide.