I've only had it once, but it was all over the tree. It's actually still recovering and I'll be amazed if it makes it through the winter, but this doesn't look like what I encountered..did you fertilize a bit to heavy on the nitrogen?
Maybe just burned tips. Take the juniper back if you can. Ask them. If the answer isn’t totally clear, get one without the brown tips or none at all. imho It’s just not worth worrying and dealing with a plant that may or may not be sick.