Thanks everyone for your suggestions. Some more clarification: I don't regularly smoke any single blend, so basically I have about 80 mason jars and dip into each on a sporadic basis. Three of my jars have small coins in them, and a lot of the coins got un-spun, which isn't the end of the world, but it's a little disappointing. I was using a regular mouth, half pint jar, which is taller than it is wide, so maybe that was part of the problem.
The one time I simply left things in the tin, the coins quickly got too dry for my liking.
I think I'm going to look for some of those shallow wide mouth mason jars that Monty55 mentioned and see if that works for the next tin I open. Otherwise I'll get a resealable mylar bag to keep my opened tins in.