Dunkin’ Donuts customers in New York and New Jersey are claiming in a new lawsuit that the company doesn’t understand how sales tax works in those states, resulting in combined overcharges worth nearly $14 million. That could buy a lot of coffee.

One complaint filed in New Jersey claims that a store in Ft. Lee charged the state’s 7% sales tax on unsweetened bottled water and bags of ground coffee, The New York Post reports, which is a violation of the law in that state [PDF].

A store near Penn Station in Manhattan also mucked up sales tax, a lawsuit [PDF] filed in federal court alleges, by charging a customer sales tax on pre-packaged coffee beans, which again, would be in violation of New York law [PDF].

“Dunkin’ should stop dunking their customers and provide customers with refunds or discounts so they are made whole,” the lawyer who filed the suits told The Post, adding that a dozen different Dunkin’ Donuts locations overcharged customers about 70% of the time.

He says Dunkin’ stores reaped $10 million from overcharging New York customers, and $4 million from improperly applying sales tax in New Jersey over three years.

Dunkin’ Donuts says its corporate office is in the process of reaching out to franchisees to investigate the issue, a spokeswoman told The Post.

Dunkin’ Donuts stores accused of overcharging customers [The New York Post]

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