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 $71.34   9.496%   $78.1144   $78.11   $78.10   $78.10  
  Purchase #2 $240.64   5.389%   $253.6081   $253.61   $253.60   $253.60  
  Purchase #3 $65.61   7.687%   $70.6534   $70.65   $70.65   $70.70  
  Purchase #4 $62.54   10.186%   $68.9103   $68.91   $68.90   $68.90  
  Purchase #5 $154.60   3.306%   $159.7111   $159.71   $159.70   $159.70  
  Purchase #6 $247.37   9.376%   $270.5634   $270.56   $270.55   $270.60  
  Purchase #7 $123.40   7.285%   $132.3897   $132.39   $132.40   $132.40  
  7 purchase totals = $965.50       $1,033.9504   $1,033.94   $1,033.90   $1,034.00