Here's a quicker way. Do whatever search you want, then scroll down on the left side and click "Sold Items". This will automatically check the "Completed Items" as well (items that ended but didn't sell). Here's a picture of where it's located.

Keep in mind that you can save searches (I have about 60 in my list as we speak), so if you're wondering what something you're actively searching for sold for in the last 90 days, just re-run your saved search and click the sold button.

Hope that helps.