The Today's total is charging a few cents extra than what the monthly payments will be and that is to make sure the next 11 payments will evenly pay off the full balance. So here is how the math works out.

11 * $8.33 + (today's total of $8.37) = $100

The initial payment is 8.37 but the remaining 11 payments will be 8.33 to pay off the $100 plan in the next 11 payments.