If there is a small (one company/property) area of commercial (or similar) landuse within an otherwise residential area, you can still decide to use landuse=residential for the outline of the whole larger area as a preliminary solution. You could later draw a separate area tagged with landuse=commercial for that commercial establishment.
The landuse tag is mostly used for larger areas and not at parcel granularity; as described above, a single shop in a residential area might not always warrant an extra "commercial" landuse.