I'm suspicious of one thing though.
You seem to be putting this calculation in the change event for the TOTAL.
Yet, the TOTAL doesn't get changed until you manually change the TOTAL.

Do me a favor... put  a msgbox in the total change event.
Then change one of the other values  and see how many times the Total change
event is being called.
For what you describe, there really shouldn't BE any change event
associated
with the Total textbox, there should only be change events with the other
textboxes.

Just make sure it's being triggered when you want and expect it to, not
unpredictably. Otherwise, you could end up with incorrect results.