Kata

What people think of as "significant" varies from human to human, but when developing your heuristic keep these things in mind:

Sweden has 1, 5, and 10kr coins; and bills for 20, 50, and 100kr; although the 50 isn't used very often.

One thing to note is that as the bill gets more expensive, the idea of what is "siginificant" for rounding up changes.

This is equivalent to not providing any clear specs: what is the cutoff point between the next round-up interval? The kata expects this:

bill < 100: 10
bill < 1000: 20
otherwise: 100

But it could easily be the total bill with 5% accounted for, since that'd be the actual least paid amount.

Again, this information is crucial to solving the kata but is being intentionally held back.