Python while loop only prompting for number twice

SENTINEL = 0
TAXRATE = 0.0625
numItems = 0
subTotal = 0

print("""/
This program will prompt you for the items you purchased online
until you enter the sentinel value of 0 to stop the process. The
program will create a running total of the items.\n\n\n""")

itemCost = float(input("Enter the price of the item(0 to stop):"))


while itemCost != SENTINEL:
    if itemCost < 0:
        print(f'this price is illegal!')
    else:
        numItems+=1
        subTotal+=itemCost
    itemCost = float(input("Enter the price of the item(0 to stop):"))

    if numItems > 0:
        salesTax = subTotal * TAXRATE
        totalCost = subTotal + salesTax
        print(f'The number of items purchased is {numItems}')
        print(f'The sub total is {subTotal:.2f}')
        print(f'The sales tax is {salesTax:.2f}')
        print(f'The total cost is {totalCost:.2f}')
    else:
        print(f'You need to purchase items!')