That thing doesn't work. Or maybe I'm using it wrong - how do you get a flight for the "total" that it lists?

Just testing it, I put in my airport and clicked a couple of international boxes... it came up with Guatemala City for $220 base, $321 Total as my lowest fare. I clicked on it and selected both arrival and departure dates that listed "$321" and when I hit "ok" it pulled up the checkout screen where my total was suddenly increased up to $478...

So what do I have to do to get the $321 that it says the price should be? (not that I'm going to buy this particular ticket, but it would be nice to know for when I'm setting up my next trip. Otherwise what's the point if it's not possible to get the price that it lists?)