> Many ways to do this 2 are:
> 1. I never put the invoice total in. I always retotal the items.

That is in the perfect world ;) in the true world most of the time need to "denormalize" the data for speed optimization

> 2. You are in control of the COMMIT command. Why don't you call an SP to
> total just before the commit. (instead of triggers)

Because the database is use by more than one software, and hard to control all the software that they do correctly the job (this why we invent trigger :)