George,
Find a tire dealer that handles that brand and see if they will do an adjustment. At best it will be pro rated based on the tread depth remaining. Given the age of the tires, and the fact that you aren't the original owner (the dealership was), they might not be willing to help you.
From the photo, this looks like it is a private brand tire, but the DOT number tells me it is made by Goodyear. That may be helpful if you can't located a retailer of the brand - you might be able to call Goodyear's 800 number and negotiate something.
From my experience these cracks are the result of some problem with the various rubber interfaces. For example, this crack could be where the white rubber and the black rubber come together (but the cracks are a bit too low for that) or the rim strip / sidewall junction (and normally these don't develop cracks) - and those are a few of the many tire related causes, and there are external cuases as has been mentioned - underinflation, rim width, etc.
These cracks are normally not a problem, as the cracks will grow until they reach the ply layer and then grow along the surface of the ply. Eventually, the rubber sidewall will fall off, leaving the plies and the structural stuff of the tire intact. But there are a few situations where the cause is not the rubber interfaces - it is a structural problem - and those can grow THRU the ples - very bad. How to tell the difference?
Structural cracks will be jagged and perhaps on a diagonal. Yours are smooth and circumferential.