Uniconta has a system account to handle rounding differences where the total of all VAT lines is not exactly equal to the VAT on the total amount before VAT. This can create a rounding difference of a few cents. If the company has not set up a 'VAT rounding' system account then Uniconta will post these differences directly on to the VAT account.
This VAT rounding system account should be set up in the chart of accounts to avoid direct postings on the VAT account.
Read about the VAT rounding system account here.