Why would you wish to cancel a job before collecting your Jobs? There are few reasons, actually. For one, you may run out of Goods while still wanting to play the game right now, and don't want to wait another hour (or more) for your orders to clear normally. Or, you may be given a quest that asks you to "start" a specific number of orders, but don't want to wait for them to complete regardless. In all of these cases, being able to cancel currently active orders is a pretty neat ability.

To cancel an order, you'll want to head into the Good Emporium's menu as though you were going to order more Goods, and then look for the red X in the top corner of each order bay, as seen below. As you can see below, I have two orders that will take almost two hours to complete, but I need Goods right now. I can simply click on that X button to cancel and order and place the five minute order instead.

Unfortunately, there isn't a confirmation window for this ability, so if you accidentally click on it, you'll cancel the order without really meaning to. Also, you won't receive your coins back, so take that into account before actually canceling an order.