But every store in that business would see their labor costs rise proportionately, so the net effect would be zero. If Walgreens' costs go up by 5%, so will Rite Aid's, CVS's, etc. Stores will just pass on the costs to the consumers. Plus, the labor cost of stores like Walgreens are very small compared to the merchandise costs. And the high-paying jobs (Pharmacists, etc.) would not be affected anyways, since you're just raising the minimum wage.
Other than Walmart, you'd be hard-pressed to find a business where the minimum-wage employees are a significant cost item in the budget.