Tax display off by a penny for some tax rates

[lat9]

I now believe that at least part of the rounding-related issues might be due to various castings to (float).

Take a "simple" case:

A $1.00 product taxed at 0.055% with free shipping is added to the cart. On entry to the 'checkout_payment' page, the order's "Tax" improperly displays as $0.05 while the order's total properly shows $1.06.

The issue is that the value recorded in the order's tax_groups for that product is 0.05499999999999994 which, when rounded to 2 significant digits, is 0.05!

[DrByte]

The real question is: At what point should tax-related rounding occur?

Zen Cart pricing/tax calculations get rounded by the order- and shopping-cart classes and various payment methods and order-totals, so that each taxed addition (or subtraction) from an order's pricing is rounded (or not) at the hands of the module that's making that change to the order's totals.

I guess the question is whether any tax additions/subtractions from the order should be performed with or without rounding, leaving the final rounding operation to the ot_tax module.

While in the US it is typically done one way, some other countries do treat it other ways. The answer would need to start with determining whether tax is initially charged at the per-item level vs the per-item-times-its-quantity level vs the all-items-of-that-tax-class level, as that affects the initial rounding strategy. Then an order-edit module would follow accordingly.

[torvista]

I have lost count of how many threads or posts there are about rounding errors. It seems way overdue that this issue is resolved.
So, if the issue is the tax basis

whether tax is initially charged at the per-item level vs the per-item-times-its-quantity level vs the all-items-of-that-tax-class level,

In my case (Spain), tax is added on the sub-total of all items within a tax group.

What is the roadmap for resolving this - can a discussion be initiated to determine all the possible tax basis?

[lat9]

I have lost count of how many threads or posts there are about rounding errors. It seems way overdue that this issue is resolved.
So, if the issue is the tax basis

In my case (Spain), tax is added on the sub-total of all items within a tax group.

What is the roadmap for resolving this - can a discussion be initiated to determine all the possible tax basis?

Good idea! I've created this (https://www.zen-cart.com/showthread....ndling-methods) post as starting point to gather the taxation requirements (and underlying algorithms) required for the various localities.