Ok, osm.wiki/Tag:'operator=' seems a good idea. You are right, all buildings are not tax collection office. There are also customs, cadastre, vat,... Thank you.

Hi. Thank you for the feedback. I was using government=tax (in french osm.wiki/FR:Tag:government%3Dtax ). I am planning to tag all 'SPF Finances/FOD Financïen' buildings. I though it was more specific. Next step is being able to query the map to get all the Finances buildings.