How much should I charge as a private math tutor (rising senior in HS)?

I had math students that got $100 an hour to tutor freshmen algebra. 

Charge them minimum wage for Buffalo NY.

If the prospective students are in 5th grade, then your high school math, while a plus, will not be required, if you are just helping with standard curriculum.  What will matter more is your teaching skill, which is likely decent if you had success at Kumon.  There is little difference between you and an adult teacher, unless that teacher was a former 5th grade math teacher.

The going rate in my area (silicon valley, admittedly expensive) is 4x minimum wage, which works out to $60/hr.  Once you have a reputation for success, you should be able to command 4x.  You might want to start at 3x.  Try looking up tutoring in your area to validate pricing.  Craigslist will do.

Remember also to file estimated taxes if you make a lot, including self-employment tax.

If, instead, you are being asked to do enrichment for gifted children, ask another question.  They're easy to teach, and soak it up like a sponge.  But you may find yourself doing research for each lesson to keep up with them.

If you check out websites like care.com you will find that students seem to be charging $15-$30/hr which seems about right. (certified, experienced teacher charge more). So what you are comfortable with but I would say you could charge on the high end as you have experience (at Kumon) and demonstrated mastery of the subject. But if you are doing several hours a week with one family, a bit of a discount is typical. I would probable ask for $20 or $25/hr.

Whatever you charge let them know you take Apple pay. 

probably minimum wage