Acrobat form field only updates in certain situations

I created this form and so far as I have been able to tell everythings works as it's supposed to except for the field that converts the "TOTAL" into words.

Each time a new item is added, followed by unit cost and quantity, the subtotal calculates, the TOTAL updates and then if you click on the field for the next row's Box # or Description, the field where the total is given in words updates.

This is fine because customers will naturally move on to either another box number on the next row or on to a description of another item in the same box.

The issue is when the customer adds the last item to the page. They will then enter the unit cost and the quantity and that's it. They won't necessarilly click anywhere else. In that case, the words will not update to reflect the final TOTAL. If you hit "Enter", that won't update it either. And if you click on any other field in the form besides one in the Box # column or the Description column... no updating. It will ONLY update if you then click on a box # field or a description field.

Is there any way to fix this so that the actual total is reflected in words even if you take no action after entering the last item (other than closing and saving the form)?

Many thanks

m