This is because your currency, NZ$, is only divided into cents. Each line on the payment has to be rounded to the nearest cent, not the transaction as a whole. In the case you cite, two lines have fractional cents that will round up. Since this is a cash transaction, that means you had to have paid in actual dollars and cents, so you should enter amounts that produce a total in dollars and whole cents. Your rounding amount is fictional anyway, so adjust it so the total matches what you paid.