Adding input ideally only to philosophy: order total I see as related to the transaction and cost to customer, the entirety of the ot_XXXXX "utilities" offers operations against previously calculated (by whatever means) values such that operations can occur to the store after determining the customer's cost: e.g. non priced "awards" not yet available for spending, discounts or additional fees. The position of that feature being dependent on its basis for determination and impact.

I see two topics in discussion though perhaps neither do directly stated: one size to fit all (code completely address all things for all conditions even when all are in one transaction) and user error in making adjustments. Neither of these can be immediately fully resolved. I have seen that homework was being done to attempt to identify all (most) reasonable configurations; however, even within each proposed condition localities and nations have yet more complexities.

As to user error, there is instruction (at many places and by many ways) or as proposed more of a lock down to force the software to work the "Zen Cart" way which I perceive to do no more than identify the need to find something else with less imposition. A psychological affect may be to encourage more discussion about how else it should be done, but at what cost?

As to JPY, I've previously looked at how that currency is handled and as memory serves, forcing to a unruly value sends to happen too early in the transaction calculations and almost too abruptly. My not knowing associated currency/business requirements prevented me from making any useful suggestions.

The penny issue unfortunately does happen also with cash transactions though not always as evident to the shopper as when looking at a breakdown on screen or shortly after ordering. An example I have was that once I was in line at a vendor that sold one product and that could be purchased in multiple quantity. While in line I saw someone buy a quantity of one followed by someone purchasing a quantity of two. The per item cost was less in a quantity of two because of tax and associated rounding. I had considered purchasing the second later but as a customer it would cost me more, even if only slightly.

Lastly in mind at the moment, I realize it appears the discussion is centered around the invoice (a document made available after making the purchase) it seems the same philosophical process to get to the same result could be applied earlier in the purchase so that the customer has consistent information through the entire process. As to list change, it seems to me that the customer "experience" should be paramount and that whether the owner has to internally adjust to be in compliance on a per purchase or some periodic basis that it is a cost of doing business even if those same owners are customers (not directly paying) to Zen Cart.