Thanks! code is well structured. Thank you for comment "# counter_1 & counter_2 produces a counter with the lowest count for each key".
It seems like "track of 100s" is good in practic - to know total bank count.

I really like this solution! I think it should be the top solution for this kata.

One tweak:
Since you're using a collections.Counter object, you don't need to initialize with values.
You could replace bills = Counter({25: 0, 50: 0, 100:0})with bills = Counter().

Even though it isn't correct, it is quite a funny hack ;)