Is there a way to round to 2 decimals in a query-of-query on an avg statement? I could not find a system function in the adobe docs.
Not in QoQ, no. The full docs for QoQ are here: "Query of Queries user guide". That includes the entirety of QoQ's functionality.
You're just gonna have to do the rounding when you're using the recordset.
It might be worth raising a ticket on the bug tracker to get an enhancement for this: https://bugbase.adobe.com/. It's functionality I've needed in the past.