Calculate shipping cost
I would not hard-code the fee logic, but instead store it as pure data. It's easier to maintain, even allowing to load it from a file.
Then, it boils down to a range-based lookup, which is quite classical (cf HLOOKUP in spreadsheet software, with so called "approximate search").

In Python, we can perform such a search via bisect, relying on lexicographic order (and infinity as an unreachable upper bound).

Separated core logic would look like :

from bisect import bisect

#For each country, list of (x,y) = (cost_threshold, fee)
#For first x such cost &lt;= x, pick y for fee.
inf = float("inf")
shippingFees = { 'USA' :    [ (50, 6), (100, 8),  (150, 10), (inf, 0) ],
                 'CANADA' : [ (50, 8), (100, 10), (150, 12), (inf, 0) ]
               }
#Make sure it is sorted (required for lookup via bisect)
#FIXME : Actually it would be better to assert it is already sorted,
#        since an unsorted input might reveal a typo.
for fee in shippingFees.values() : fee.sort()

def getShippingFee(amount, country):
   fees = shippingFees[country.upper()] #raise KeyError if not found.
   idx = bisect(fees, (amount,) )
   return fees[idx][1]




Update

Here is a sample of "working application" using the helper function, assuming you have saved the code snippet above as prices.py (which should be stored in a module, but that's another story).

NB : I have dropped the exit part, since I don't like to type no when I can hit CTRL+C.

#!/usr/bin/python2
""" Your description here """

from prices import getShippingFee

print('This will calculate shipping cost and your grand total.')

while True:

   #TODO : proper input processing, python3 compatible.
   totalAmount = float(raw_input('Enter your total amount: ').replace(',', '').replace('$', ''))
   country = raw_input('Type "Canada" for Canada and "USA" for USA: ').strip().upper()

   try :  #TODO : proper country check.
      shippingFee = getShippingFee(totalAmount, country)
      grandTotal = totalAmount + shippingFee
      if shippingFee :
         print('Your shipping cost is: %.2f' % shippingFee)
      else :
         print('Your shipping is free!')
      print('Your grand total is: %.2f' % grandTotal)

   except KeyError :
      print ("Sorry, we don't ship to this hostile country : %s" % country)