You can use the dollars and merits systems at the same time! For example, you could use the merits system for all positive behaviors and use the dollars system for all negative behaviors, and this will give you two separate totals that do not count against each other.
When using both systems your school dashboard will have both dollars and merit averages:
You can choose which behavior total you want to see on the Leaderboard:
You can also show both behavior totals on your weekly Character Report: