Some restaurants charge a 10% fee on the food consumed.

Answer

If the customer was aware of the 10% charge on the food, then it will not be riba. Since the customer was made aware of the 10% it is merely part of the food's price regardless of the purpose for which the restaurant will be using the money for. If he patronizes the restaurant, it will be tantamount to him accepting the additional charge as part of the food's price, since before ordering the food he has been made aware of the 10% charge. Despite the fee not being riba, it is morally improper to impose the fee as a separate item.