How do you store a partially used vial upright?

I received a 5 mg vial but only want to take half the dose. The problem is, when I put it back in its box, it keeps tipping over - and I can’t figure out a good way to keep it upright.

Does it actually need to stay upright, or does it not matter? And is there any risk of the remaining liquid leaking?

(Please keep replies focused on storage — not interested in the multi-use debate.)