longwave's suggestions in #1153086: Inclusive tax not visible in cart block or checkout pane have got me thinking - it would be nice if calculated line-items could also display a different value, either by adding a similar display_value field, or by providing a 'format' callback for the defining module which would control the display, but not the total.

My use-case for this is for coupons that apply to tax-inclusive products. We want the total discount on the order to be the face value of the coupon - however, to get this we have to count only a portion of the face value as a discount to the products--the rest is accounted for by the corresponding decrease in tax. But it could be confusing to customers to see the coupon line-item disagree with the face value.