Since you live in California, any gasoline cans you order will have to be CARB-rated (unless the business you’re ordering from doesn’t really care about state regulations). CARB-rated cans are designed to vent any excess vapors automatically when too much heat causes the pressures to rise.

Keep in mind, however, that gasoline vapors are heavier than air. The vents at the top of the shed may not do as much good as you would like unless there is really good air circulation in the shed. It is recommended that gasoline storage enclosures be vented at the bottom. Fortunately vents are pretty easy to add to a structure (unless it’s concrete or in a basement or something, which I doubt).