Hi Berta.
First option with article hierarchy would have been w/o development.
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I see an option for you to check. My hypothesis is that you don't want a Price point rounding for ALL the articles with fixed Price in the article master data.
In tcode OWV6 customizing of sales Price determination sequence (VKERV), you can define steps, rounding to Price points, and requirements.
Check Sales Price Determination - SAP Retail - SAP Library
I don't know which VKERV(s) you are using but my idea is the following for each ones:
* see with a developer to code a requirement that will set sy-subrc = 0 (success) when the price calculation concerns an article with a fixed price (2) defined on the sales area.
* define specific sales pr. Det. Seq (you may copy the ones actually used) in tcode OWV6.
* define for each step (already existing) a previous step identical, except that this new step will NOT be marked for Price point rounding and you will set this step with the requirement coded on stage 1.
Let me know if it helps.
Regards.
David