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 $127.26   4.205%   $132.6113   $132.61   $132.60   $132.60  
  Purchase #2 $70.61   8.593%   $76.6775   $76.68   $76.70   $76.70  
  Purchase #3 $234.42   11.568%   $261.5377   $261.54   $261.55   $261.50  
  Purchase #4 $210.86   12.550%   $237.3229   $237.32   $237.30   $237.30  
  Purchase #5 $200.80   11.800%   $224.4944   $224.49   $224.50   $224.50  
  Purchase #6 $112.95   10.420%   $124.7194   $124.72   $124.70   $124.70  
  Purchase #7 $182.50   3.861%   $189.5463   $189.55   $189.55   $189.50  
  7 purchase totals = $1,139.40       $1,246.9095   $1,246.91   $1,246.90   $1,246.80