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 $68.93   7.413%   $74.0398   $74.04   $74.05   $74.00  
  Purchase #2 $132.56   5.103%   $139.3245   $139.32   $139.30   $139.30  
  Purchase #3 $70.98   10.516%   $78.4443   $78.44   $78.45   $78.40  
  Purchase #4 $169.71   4.829%   $177.9053   $177.91   $177.90   $177.90  
  Purchase #5 $136.25   7.420%   $146.3598   $146.36   $146.35   $146.40  
  Purchase #6 $107.85   5.117%   $113.3687   $113.37   $113.35   $113.40  
  Purchase #7 $221.27   11.365%   $246.4173   $246.42   $246.40   $246.40  
  7 purchase totals = $907.55       $975.8597   $975.86   $975.80   $975.80