Royalty regarding cryptocurrency.

If a project receives profits from in-game marketplace transaction fees with cryptocurrency, how would I as a founder tackle the subject of royalty?
When it comes to fiat currency it’s pretty straightforward, but I’m kinda lost when it comes to crypto especially when it comes to the volatility of the coin/token.
Would appreciate any additional information about it or if I can be directed somewhere to discuss it in more detail.

For taxation purposes, accountants are happy with an average yearly rate for currency, as long as you get it from a recognized source.