Why does my Python code only add up the price of the last item in my shopping cart?

So I am trying to make a python code that lets you add items to your shopping cart then once you type "done" it is supposed to add up the prices of each item you added to your shopping cart and then tell you the total price.

My issue is that once I type "done" it only adds up the price of the last item that I added to my shopping cart then prints it out.

shopping_cart = [""]

food = shopping_cart

#Stock
stock = {
    "\nFruit\n\n"
    "banana": 50,
    "apple": 15,
    "orange": 32,
    "pear": 15,

    "\nDrinks\n\n"
    "apple juice": 10,
    "orange juice": 10,
    "pinapple juice": 10,
    "milk": 15,

    "\nSnacks\n\n"
    "chips": 20,
    "cookies": 20,
    "chocolate": 25,
    "lollies": 50
}

#Prices 
prices = {
    #Fruit
    "banana": 10,
    "apple": 5,
    "orange": 5,
    "pear": 5,

    #Drinks
    "apple juice": 5,
    "orange juice": 5,
    "pinapple juice": 5,
    "milk": 4.80,

    #Snacks
    "chips": 7,
    "cookies": 4,
    "chocolate": 6,
    "lollies": 5.50
    
}

#Loop
while True:
    item = input("\nEnter an item: ").lower()
    shopping_cart.append(item)

    if item == 'done':
        break

    if item == 'cart':
        print(shopping_cart)

    if item == 'stock':
        for k, v in stock.items():
            print(k + ":", v)


#Define the bill variable
def shopping_bill(food):
    total = 0
    for key in prices:
        for key in stock:
            for item in food:
                if item == key in prices:
                    total += prices[key]
        break 
    print("Your bill total equals $", total)
    print("Thank you for shopping at B&K Supermarket!")

shopping_bill(food)

>Solution :

Mostly the same as the other answer but checks that the stock doesn’t go below 0.

shopping_cart = []

food = shopping_cart

#Stock
stock = {
    #Fruit
    "banana": 50,
    "apple": 15,
    "orange": 32,
    "pear": 15,

    #Drinks
    "apple juice": 10,
    "orange juice": 10,
    "pinapple juice": 10,
    "milk": 15,

    #Snacks
    "chips": 20,
    "cookies": 20,
    "chocolate": 25,
    "lollies": 50
}

#Prices 
prices = {
    #Fruit
    "banana": 10,
    "apple": 5,
    "orange": 5,
    "pear": 5,

    #Drinks
    "apple juice": 5,
    "orange juice": 5,
    "pinapple juice": 5,
    "milk": 4.80,

    #Snacks
    "chips": 7,
    "cookies": 4,
    "chocolate": 6,
    "lollies": 5.50
    
}

#Define the bill variable
def shopping_bill(food):
    total = 0
    for key in stock:
       total += food.count(key) * prices[key]
    print("Your bill total equals $", total)
    print("Thank you for shopping at B&K Supermarket!")

#Loop
while True:
    item = input("\nEnter an item: ").lower()


    if item == 'done':
        shopping_bill(shopping_cart)
        break

    if item == 'cart':
        print(shopping_cart)
        next

    if item == 'stock':
        for k, v in stock.items():
            print(k + ":", v)
        next

    for key in stock:
       if item == key:
              if stock[item] > 0:
                     shopping_cart.append(item)  
                     stock[item] -= 1
                     print("added to cart")
              else:
                     print("out of stock")