"my mathematical brain hates that I need to round this"

It isn't rounding, casting to int chops the decimal bit off.

I'm expecting no because you can't make 75 with two notes of 50

Are you expecting "YES" or is the test expecting "YES"

Am I being thick? I put this in for the test case: {25, 25, 50, 50, 100};

Expected: "YES"
But was: "NO"

Why is "YES" expected?
25 goes in till, one 25 bill change - YES
25 goes in till, two 25 bills change - YES
50 goes in till, one 25 bill change and one 50 bill change - YES (minus one 25 bill change)
50 goes in till, two 50 bill change - YES (minus one 25 bill change)
100 can't go in till, the two 50 bills can't make the 75 required change?