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 $250.77   4.387%   $261.7713   $261.77   $261.75   $261.80  
  Purchase #2 $235.83   10.587%   $260.7973   $260.80   $260.80   $260.80  
  Purchase #3 $246.91   8.596%   $268.1344   $268.13   $268.15   $268.10  
  Purchase #4 $40.58   13.280%   $45.969   $45.97   $45.95   $46.00  
  Purchase #5 $124.62   6.143%   $132.2754   $132.28   $132.30   $132.30  
  Purchase #6 $139.82   10.775%   $154.8856   $154.89   $154.90   $154.90  
  Purchase #7 $214.92   9.294%   $234.8947   $234.89   $234.90   $234.90  
  7 purchase totals = $1,253.45       $1,358.7277   $1,358.73   $1,358.75   $1,358.80