When you wish to write off small outstanding balances on customer invoices to either "Discounts" or "Allowances", the best solution is to create a zero dollar check for the customer.   The steps to perform this process is as follows:

1.  Create payment record for customer at zero dollars
2.  On the payment distribution screen, add a record for each invoice that needs to be cleared
     Change the Dist Amount = 0
     Enter the remaining amount due in either "Discount" field or "Allowance" field
3.  Post customer payment

Note:  You can also override the account number designated for Discounts or Allowance if needed