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 $87.33   13.232%   $98.8855   $98.89   $98.90   $98.90  
  Purchase #2 $246.29   6.133%   $261.395   $261.40   $261.40   $261.40  
  Purchase #3 $15.28   13.725%   $17.3772   $17.38   $17.40   $17.40  
  Purchase #4 $111.78   10.717%   $123.7595   $123.76   $123.75   $123.80  
  Purchase #5 $94.55   9.126%   $103.1786   $103.18   $103.20   $103.20  
  Purchase #6 $93.59   5.726%   $98.949   $98.95   $98.95   $98.90  
  Purchase #7 $246.97   8.454%   $267.8488   $267.85   $267.85   $267.80  
  7 purchase totals = $895.79       $971.3936   $971.41   $971.45   $971.40