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 $54.38   13.148%   $61.5299   $61.53   $61.55   $61.50  
  Purchase #2 $73.82   3.836%   $76.6517   $76.65   $76.65   $76.70  
  Purchase #3 $101.72   13.648%   $115.6027   $115.60   $115.60   $115.60  
  Purchase #4 $86.96   5.641%   $91.8654   $91.87   $91.85   $91.90  
  Purchase #5 $178.83   10.536%   $197.6715   $197.67   $197.65   $197.70  
  Purchase #6 $247.34   5.807%   $261.703   $261.70   $261.70   $261.70  
  Purchase #7 $62.66   6.543%   $66.7598   $66.76   $66.75   $66.80  
  7 purchase totals = $805.71       $871.7840   $871.78   $871.75   $871.90