import decimal

a = decimal.Decimal('54.12')
b = decimal.Decimal('54.00')

for n in (a, b):
    print("You have just bought an item that cost ${0:.{1}f}."
          .format(n, 0 if n == n.to_integral() else 2))

>>> import decimal
>>> n = decimal.Decimal('54.12')
>>> print('%g' % n)
'54.12'
>>> n = decimal.Decimal('54.00')
>>> print('%g' % n)
'54'

>>> dollars = Decimal(repr(54.12))
>>> print "You have just bought an item that cost ${}.".format(dollars)
You have just bought an item that cost $54.12.

round = x + 0.5
s = str(round)
dot = s.find('.')
print(s[ : dot])

>>> from decimal import Decimal
>>> print Decimal("12.00").normalize()
>>> 12
>>> print Decimal("12.54").normalize()
>>> 12.54