what is the functional use of ROUNDING_AMT in ap_invoice_distributions_all TABLE

we found in documentation:

For price, quantity, or invoice line corrections ROUNDING_AMT NUMBER Amount corresponding to rounding included in BASE_AMOUNT if any

we would like to know when this value is set in table field, if it is an user action during creating an invoice, if it is a system action when the user validates an invoice and how it is calculated

thank you