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 $241.71   9.676%   $265.0979   $265.10   $265.10   $265.10  
  Purchase #2 $234.95   5.324%   $247.4587   $247.46   $247.45   $247.50  
  Purchase #3 $217.34   4.235%   $226.5443   $226.54   $226.55   $226.50  
  Purchase #4 $185.62   11.658%   $207.2596   $207.26   $207.25   $207.30  
  Purchase #5 $222.26   10.142%   $244.8016   $244.80   $244.80   $244.80  
  Purchase #6 $241.48   8.147%   $261.1534   $261.15   $261.15   $261.20  
  Purchase #7 $12.89   3.794%   $13.379   $13.38   $13.40   $13.40  
  7 purchase totals = $1,356.25       $1,465.6945   $1,465.69   $1,465.70   $1,465.80