Buying in the Mac App Store for the enterprise
Apple also has a Volume Purchase Program for Business, which it says is applicable "whether you have ten employees or ten thousand". I didn't see anything saying it couldn't actually be used for even fewer than 10 employees/users, too. There doesn't appear to be a minimum quantity for VPP license purchases (that I could find, anyway).

If you choose to enroll, you'll need to set up a new Apple ID using an email that isn't already tied to an existing Apple ID.

You can find more information in the VPP Guide (PDF).