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 $246.71   6.102%   $261.7642   $261.76   $261.75   $261.80  
  Purchase #2 $107.64   8.843%   $117.1586   $117.16   $117.15   $117.20  
  Purchase #3 $227.31   13.271%   $257.4763   $257.48   $257.50   $257.50  
  Purchase #4 $244.95   8.850%   $266.6281   $266.63   $266.65   $266.60  
  Purchase #5 $40.79   3.759%   $42.3233   $42.32   $42.30   $42.30  
  Purchase #6 $88.68   8.167%   $95.9225   $95.92   $95.90   $95.90  
  Purchase #7 $195.31   11.225%   $217.2335   $217.23   $217.25   $217.20  
  7 purchase totals = $1,151.39       $1,258.5065   $1,258.50   $1,258.50   $1,258.50