Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.53   9.438%   $65.1484   $65.15   $65.15   $65.10  
  Purchase #2 $76.47   12.835%   $86.2849   $86.28   $86.30   $86.30  
  Purchase #3 $183.85   7.296%   $197.2637   $197.26   $197.25   $197.30  
  Purchase #4 $64.76   3.794%   $67.217   $67.22   $67.20   $67.20  
  Purchase #5 $205.45   9.394%   $224.75   $224.75   $224.75   $224.80  
  Purchase #6 $207.56   3.771%   $215.3871   $215.39   $215.40   $215.40  
  Purchase #7 $110.28   4.562%   $115.311   $115.31   $115.30   $115.30  
  7 purchase totals = $907.90       $971.3621   $971.36   $971.35   $971.40