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 $61.27   8.533%   $66.4982   $66.50   $66.50   $66.50  
  Purchase #2 $73.44   11.234%   $81.6902   $81.69   $81.70   $81.70  
  Purchase #3 $176.94   3.259%   $182.7065   $182.71   $182.70   $182.70  
  Purchase #4 $102.49   3.157%   $105.7256   $105.73   $105.75   $105.70  
  Purchase #5 $180.80   7.661%   $194.6511   $194.65   $194.65   $194.70  
  Purchase #6 $122.55   4.144%   $127.6285   $127.63   $127.65   $127.60  
  Purchase #7 $195.71   10.301%   $215.8701   $215.87   $215.85   $215.90  
  7 purchase totals = $913.20       $974.7702   $974.78   $974.80   $974.80