In customer Module -> customer View there is no way to see any sales without invoice.
In the overview tab, the Icome Graph show the income by month, and the amount if over with the mouse.
However you can't know to which transaction are related this income unless you go to search for this transaction in the banking module, or you generate a report that include the sales without invoice in the report.

It will be much easier and faster just to click on the month income bar of the graph, to show all the related transaction of that customer for the related income month.