It has a special meaning in the context of wine appreciation. This reference has a definition of "round" in wine parlance http://www.vintrinsic.com/images/Wine_Tasting_Vocabulary.pdf I am not sure if it has the same meaning as "rounded" in your sentence. "Well-rounded" is used about the character of people who are well developed, skilled, and/or emotionally balanced in all relevant aspects. For a wine, this could mean that it has a good balance of tastes. This could be what the writer means but I can't be sure.