I don't think there is a magic number of interviews to go on for matching, it's a personal thing we all need to figure out. Everybody focuses on that >90% rate of matching for people with 10 interviews, but it's really a surrogate marker that probably represents either a) people who are on the more competitive end of the spectrum so they get a lot of offers or b) people who applied broadly and were willing to go anywhere, and that came across during their interviews. Having 10 interviews does not guarantee you'll match, just like having 5 does not mean you're in bad shape. I personally know someone who interviewed at 5 and matched at their #1, someone who interviewed at 12 and matched at #12, someone who interviewed at 15 and scrambled, plus several people in between.
You need to examine your own priorities and ask yourself -
Are you in a region that is likely to keep you if you want to stay, or are you trying to go to a more popular location? Are there enough programs on your interview list that can act like "safeties" or pretty solid bets, or are there too many reaches? Do you want a big program or small program? Do you interview well or do you need a couple extra in case you get nervous and put your foot in your mouth a few times? and a whole bunch of other factors. I've found keeping a running rank list between getting offers and interviewing places is helping me figure out my priorities. They rank us often times before we interview and immediately after we interview, why not rank them that way too.
And once you sort all that out, you can figure out a number that works for you. It's definitely more about quality than quantity, but there are people who need more interviews and others who need less.
I do agree with the above poster that the earlier the better with cancellations, once you start realizing you really don't wanna interview at a certain place. I got off the waitlist 5 days before a particular interview, which has got to be a pain in the butt for program coordinators to find sometime to take that place on such short notice, and that could even hurt future applicants from your institution.
