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 $60.33   13.599%   $68.5343   $68.53   $68.55   $68.50  
  Purchase #2 $146.70   5.251%   $154.4032   $154.40   $154.40   $154.40  
  Purchase #3 $22.91   4.161%   $23.8633   $23.86   $23.85   $23.90  
  Purchase #4 $152.33   4.778%   $159.6083   $159.61   $159.60   $159.60  
  Purchase #5 $241.66   8.289%   $261.6912   $261.69   $261.70   $261.70  
  Purchase #6 $153.51   5.856%   $162.4995   $162.50   $162.50   $162.50  
  Purchase #7 $85.43   8.648%   $92.818   $92.82   $92.80   $92.80  
  7 purchase totals = $862.87       $923.4178   $923.41   $923.40   $923.40