Break Outside Loop with Previous Example

UPDATED:

This Code Works:

# North Carolina Sales Tax Estimator
# Estimates the Amount of Tax You Should Pay in North Carolina

# Defines the Current 2012 Tax Rate
nctaxrate = 0.07

# Defines the tax variable by multipling subtotal by the current nc tax rate
# tax = subtotal * nctaxrate

# Defines the total variable by adding the tax variable to the subtotal variable
# total = subtotal + tax

# Defines the Subtotal from an Input of the User's Purchase Amount
def main():
    print("\t\t\tThis is the NC Sales Tax Estimator")
    print("\t\t Input Your Total Purchases Below\n")

    while True:
        subtotal = float(input("Enter the total price of your purchases:\t$").strip())
        if subtotal == -1: break
        tax = subtotal * nctaxrate
        total = subtotal + tax

        print("\tSUBTOTAL: $", subtotal)
        print("\t     TAX: $", tax)
        print("\t   TOTAL: $", total)

# if this script is called directly by Python, run the main() function
# (if it is loaded as a module by another Python script, don't)
if __name__=="__main__":
    main()

Here is the Original Question:

So I am learning Python and asked a previous question yesterday and was supplied with an awesome set of code that I decided to modify to work with an NC Sales Tax Estimator Program I wanted to create.

The one thing is that I am getting a break out loop error that I don't quite understand. I've searched and tried to understand the meaning but I know the code worked before. Also the tax code program I created from scratch :) worked before trying to add the fancy ability to submit many inputs in a loop until the user wanted to 'exit'.

Here is the Code:

# North Carolina Sales Tax Estimator
# Estimates the Amount of Tax You Should Pay in North Carolina

# Defines the Current 2012 Tax Rate
nctaxrate = 0.07

# Defines the tax variable by multipling subtotal by the current nc tax rate
tax = subtotal * nctaxrate

# Defines the total variable by adding the tax variable to the subtotal variable
total = subtotal + tax

# Defines the Subtotal from an Input of the User's Purchase Amount
def main():
    print("\t\t\tThis is the NC Sales Tax Estimator")
    print("\t\t Input Your Total Purchases Below")

while True:
    subtotal = float(input("Enter the total price of your purchases (or 'exit' to quit) :\$").strip())
    if subtotal.lower()=='exit':
        break

    try:
        subtotal = int(subtotal)
    except ValueError:
        print("That wasn't a number!")

    try:
        print("\tSUBTOTAL: $", subtotal)
        print("\t     TAX: $", tax)
        print("\t   TOTAL: $", total)
    except KeyError:
        print("")

# if this script is called directly by Python, run the main() function
# (if it is loaded as a module by another Python script, don't)
if __name__=="__main__":
    main()

P.S. I only added the KeyError because I researched that you must have an error statement after a try. I'm just a beginner so I'm attempting to create programs myself and reading "Python for the Absolute Beginner".

UPDATE:

I fixed the indentation but now I get the following traceback error:

Traceback (most recent call last):
  File "C:/LearningPython/taxestimator.py", line 30, in <module>
    tax = subtotal * nctaxrate
NameError: name 'subtotal' is not defined

I thought I defined it in the input ie.

subtotal = float(input("Enter the total price of your purchases (or 'exit' to quit) :\$").strip())

Is it because the other defines (tax and total) that use the defined subtotal are defined before subtotal is defined? I tried moving them below the defined subtotal but it didn't work still.

Thanks for any Advice.

Best,

Steven