What's your experience with Pirate Ship "adjustments"?

I ship quite a bit using Pirate Ship. Most of the boxes I use are from Uline and are marked on the bottom 15x15x7, 15x15x12 etc. Those are the two sizes I use most. I also always round up regarding weight. Dozens of these boxes have made it through with no issue except lately, when I have been getting dinged with regards to the pre-printed box dimensions. My 15x15x7 boxes are being charged 16x16x8 and the 15x15x12 is being charged 16x16x13. PS says UPS uses a "machine" that reads the dimensions. IDK, my friend says that UPS probably has an issue with Uline. 

Pirate Ship is awesome I use them all the time.

@nogaps 

"Don’t spend it all in one place".

I’ll have to look into Pirate Ship, didn’t know about them.

Of course round up, who needs more trouble in their life. Unless, you are repeatedly shipping and it adds up. Even then ...

I like that it get’s automatically paid, rather than me paying separate supplementary bill to FedEx, which included a $4.50 service fee for them collecting the tariff.

On the matter of weight, I always round up to at least the nearest pound, as my scales are not calibrated or certified. Same for size, I always round up to the nearest inch. I've never any issues with either PS or their contractors, and I've shipped or had shipped small items as well as items up to 100+ pounds (both as sender and receiver).

I know a manufacturer that swears by Pirate Ship.  Says it has saved them a lot of money in shipping costs and can also be effective when shipping overseas.  I have not yet tried it.

On the subject of upcharges, a large UPS distribution near me recently closed their customer counter so I began using a nearby UPS Store for shipping.  I quickly realized that I was consistently being charged significantly more than the estimate provided by the shipping calculator software on the UPS website.  This had never happened over the many years that I shipped from the customer counter within the UPS distribution center.  When I questioned the UPS Store manager/franchise owner about it, she said they had to upsize the package dimensions or UPS would send them a "surcharge after the fact", not unlike that reported by the OP. 

The final straw for me was when, even after I began upsizing my dimensions, the UPS Store wanted to charge me about 50 percent (about $60) above the UPS website shipping estimate for a shipment and, when I questioned the manager/owner to understand why, I was told the address wasn't on the UPS driver's regular ground route.  When the counter representative told the manager/owner that it was an air shipment, not a ground shipment, the manager/owner tried to make up a different excuse.  I walked out of their store with the package and drove to the nearest FedEx store where the cost of shipping was about half what the UPS Store wanted to charge me, and even less than the estimate from the UPS website. I have not shipped using UPS since.