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 $222.99   4.117%   $232.1705   $232.17   $232.15   $232.20  
  Purchase #2 $126.39   5.523%   $133.3705   $133.37   $133.35   $133.40  
  Purchase #3 $141.29   9.443%   $154.632   $154.63   $154.65   $154.60  
  Purchase #4 $190.53   7.291%   $204.4215   $204.42   $204.40   $204.40  
  Purchase #5 $49.51   5.872%   $52.4172   $52.42   $52.40   $52.40  
  Purchase #6 $97.43   9.843%   $107.02   $107.02   $107.00   $107.00  
  Purchase #7 $23.25   4.374%   $24.267   $24.27   $24.25   $24.30  
  7 purchase totals = $851.39       $908.2987   $908.30   $908.20   $908.30