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 $62.86   5.853%   $66.5392   $66.54   $66.55   $66.50  
  Purchase #2 $168.99   8.789%   $183.8425   $183.84   $183.85   $183.80  
  Purchase #3 $249.68   4.821%   $261.7171   $261.72   $261.70   $261.70  
  Purchase #4 $46.67   4.615%   $48.8238   $48.82   $48.80   $48.80  
  Purchase #5 $182.75   3.787%   $189.6707   $189.67   $189.65   $189.70  
  Purchase #6 $27.65   11.811%   $30.9157   $30.92   $30.90   $30.90  
  Purchase #7 $84.40   9.633%   $92.5303   $92.53   $92.55   $92.50  
  7 purchase totals = $823.00       $874.0393   $874.04   $874.00   $873.90