Hello. I've recently made an offer on a property and the attorney review has been successfully closed. Unfortunately, I received the property survey AFTER the close of the attorney review and found out that the actual lot size is 1.38 acres, and NOT 1.5 acres as declared on the listing.

Is this rounding up common? Should I be re-negotiating the offer price?

Yes rounding in ads is common. You can try to renegotiate, but I'm assuming you viewed the property. If you have, then you were satisfied with the property as viewed. An extra .12 acres shouldn't make much of a difference.