The promotions module rounds discounts in up to 3 significative digits, which can, in very specific scenarios, amount to slight divergences in the final price of a cart.

For instance, let's say we have the following, example scenario:

Item 1 - $10 Item 2 - $20 Item 3 - $32

Total - $62

And 2 promotions applying in all of them:

Promotion A - $15 OFF Promotion B - 10% OFF.

Usually, the discount to be calculated is sequential, with the nominal value off coming first:

$62 - $15 = $47 Then $47 * 0.9 = $42.3

However, the discounts are distributed, even for the nominal discount, proportionally in the cart, so what really happens is:

item 1: Original value = $10 Nominal discount (15 * 10/62 of the cart) = -$2.41935484 Percentual expected discount (12.5806452 * 0.9) = -$1.25806452 Percentual real discount = -$1.258

item 2: Original value = $20 Nominal discount (15 * 20/62 of the cart) = -$4.83870968 Percentual expected discount (15.1612903 * 0.9) = -$1.51612903 Percentual real discount = -$1.516

item 3: Original value = $32 Nominal discount (15 * 32/62 of the cart) = -$7.74193548 Percentual expected discount (24.2580645 * 0.9) = -$2.42580645 Percentual real discount = -$2.426

🔎 total diference: 0.00006452 + 0.000012903 + 0.000019355 = 0.0000270973

We can see, above, that a "micro" difference was created.

If, several items were added, with distinct prices, to this example cart, this difference could amount to 1 cent (0.01) or more.

There are a multitude of ways to eventually recreate the case Fortunately, all of them are extremely specific.

Given that, it's hard to replicate the issue, but, mostly, it's necesary to create a cart with several (~10+) different items and all of them with 2+ promotions, ideally, one of them being a nominal discount and the other one, a percentual discount.

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