Taxes don't require even High School level Math, much less something like trigonometry or high-level algebra.

You overestimate the minimum level of math required to graduate high school (in the United States).

When I went to school (about 20 years ago, at a suburban school in the North East), to graduate, you need to pass 6 semesters of math. You could achieve that by taking:

• Algebra 1 (2 semesters): very basic algebra
• Geometry (2 semesters): not sure if the remedial level covers proofs or it is just memorizing the names of shapes and how to calculate the area of them
• 2 math electives: very basic classes like Problem Solving, a class that teaches students how to read word problems and apply basic math skills to solve them