First, you can not go by the thumbnail images on the page with your photo-those are rounded out examples. You have to go by the PDF sales sheet, which is located under the info on the right. Open that and it will give you the exact prices. And even then, you should go to the page as a buyer, in other words, log out then go see what the sales sheet says.
All your images have the same pricing for the same sizes. There are no differences image to image with identical sizes-I checked. And the linked image you have here may just be an anomaly that would not have anything to do with sales. Looks like you're actually ok across the board and reading way too much into the rounding of price points on the thumbnails.