Shares of Australia’s Domino’s Pizza Enterprises Ltd. tumbled the most in about six months as the struggling fast-food chain reported a further decline in sales across several markets. The stock fell as much as 13%, the most since February, after a sales slump accelerated in the financial year ending June 30. Same-store sales dropped 4.1%, while all of its key markets across Australia, Europe and Asia reported declines, the company reported Wednesday.