If there's smell, then there's gasoline in the air.
I am not an expert, but it sounds to me like a dangerous situation, like it could favor an explosion.
I'm not crazy about it, and only do it if I have some reason to need extra gasoline without returning to the gas station. It's not something I do often. In those cases, I get the can out of the trunk as soon as I can, and put it in the garage (which is more easily ventilated than a car trunk). There was some impending crisis, don't recall which one it was (may have been a looming hurricane), a few years back, during which I kept 5-10 gallons of gas in my garage, as I anticipated shortages. It ended up not happening, and I simply used the gas and washed out the cans.
I wouldn't go around as a matter of course with an extra five gallons of gas in a can in the trunk of my car, let's put it that way. Keeping the tank in my late father's Cadillac (which I rarely drive, it has several mechanical issues and guzzles gas, 14 MPG and that's probably being generous, get it out for a short ride once a week to keep the battery charged, also use it to haul things as needed) filled up, and parked in the garage, is my "gas storage" method. I could siphon it out if I had to.