In Canada, I have the means to search $5s. There are 100 notes in a bundle. I search for fancy serial numbers and unc notes. I got a price guide and found out there are replacement and low printed notes to look for, I've found lots of good stuff.
My advice is to buy a book and it will say what to look for. You decide what you keep. It is very costly and most of the notes in circulation aren't in the best condition. It like crh can be very streaky, I've went from a few weeks of absolutly nothing to two rotator notes in one week (I haven't found one since). Don't get discouraged.