How clear is the engraving? Even if it is clearly Hanes, someone somewhere could have made an error in transcribing a name. There was a Ham's Mississippi Cavalry. Company B was from Tishomingo County. John Spain is listed as a member of this company. Is this your man?
Also, Rowland's (see site below) account of the 1st Miss Cav. refer's to a Haynes as a company commander. I don't know which company or where they were from.
Hope this helps.