I would rather recommend using an arbitrary precision decimal library like Decimal.js, and using strings to represent money in JSON. And of course using an appropriate database type for storing the data.
Edit: And sum your (optionally price-weighted) time first.
What you gain by consistently using an arbitrary precision decimal library to process all monetary values, is the freedom to process smaller fractions later if necessary. Also you'll never overflow with really big values.
In other words, when you represent monetary values with arbitrary precision Decimal objects everywhere, you can easily expand your application as much as you want on either side of the decimal dot. Changing existing integer-based code do to that is very error-prone, you quickly lose sight of what exactly an integer value or parameter means in different places.