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 $119.77   10.706%   $132.5926   $132.59   $132.60   $132.60  
  Purchase #2 $114.34   8.533%   $124.0966   $124.10   $124.10   $124.10  
  Purchase #3 $148.28   11.751%   $165.7044   $165.70   $165.70   $165.70  
  Purchase #4 $45.71   3.626%   $47.3674   $47.37   $47.35   $47.40  
  Purchase #5 $249.96   4.548%   $261.3282   $261.33   $261.35   $261.30  
  Purchase #6 $65.69   7.119%   $70.3665   $70.37   $70.35   $70.40  
  Purchase #7 $71.49   3.169%   $73.7555   $73.76   $73.75   $73.80  
  7 purchase totals = $815.24       $875.2112   $875.22   $875.20   $875.30