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 $54.44   9.220%   $59.4594   $59.46   $59.45   $59.50  
  Purchase #2 $127.63   13.397%   $144.7286   $144.73   $144.75   $144.70  
  Purchase #3 $34.41   8.464%   $37.3225   $37.32   $37.30   $37.30  
  Purchase #4 $115.58   9.251%   $126.2723   $126.27   $126.25   $126.30  
  Purchase #5 $179.80   7.787%   $193.801   $193.80   $193.80   $193.80  
  Purchase #6 $246.71   6.176%   $261.9468   $261.95   $261.95   $261.90  
  Purchase #7 $126.62   8.800%   $137.7626   $137.76   $137.75   $137.80  
  7 purchase totals = $885.19       $961.2932   $961.29   $961.25   $961.30