We use QB 2017 Desktop and most of our purchases are expensed to a job.
Write a check to the gas station, and in the customer:job field you would enter the customer.
Easiest thing to do is when they turn their receipts in, they write the job name on the receipt.
IMO this is a pretty minor thing to track per job. I would not bother. $30 per fill up gets us through 3-5 days of installs. $30 on a week long install is a drop in the bucket. Plus mix in service calls or a stop at another client and there is no way to tell how much fuel was actually used per job. Not to mention how fuel was in the truck before the jo started etc.
We expense all trips to Home Depot, parts, etc to clients. But I also know when my crew buys conduit fittings, screws, anchors etc, some of those materials are getting used on future jobs. I also know they are using items that were expensed to prior projects.
Our projects are flat bids, so the client does not get billed. This just helps figure profit per job. But if you try to calculate it down to the penny, you are going to spend more time and money than it's worth.
It just dawned on me, instead of tracking fuel purchases, keeping a log of mileage would be much better. Anytime your tech moves the van, he logs where he is going. Probably be a pain to enforce