format python arredondamento print

1>>> a=13.946
2>>> print(a)
313.946
4>>> print("%.2f" % a)
513.95
6>>> round(a,2)
713.949999999999999
8>>> print("%.2f" % round(a,2))
913.95
10>>> print("{0:.2f}".format(a))
1113.95
12>>> print("{0:.2f}".format(round(a,2)))
1313.95
14>>> print("{0:.15f}".format(round(a,2)))
1513.949999999999999