Given that this is Norway, the cynic in me thinks this is not about getting better demographic data as claimed, but rather to lay the groundwork for progressive

Given that this is Norway, the cynic in me thinks this is not about getting better demographic data as claimed, but rather to lay the groundwork for progressive sales taxes: your sales tax rate (potentially only for certain items) increases relative to your income and/or consumption habits. If this were just about demographics, it would be relatively straightforward to anonymize purchase records. (Massive privacy implications aside, I don't necessarily disagree with progressive sales taxation.)