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 $68.33   7.138%   $73.2074   $73.21   $73.20   $73.20  
  Purchase #2 $229.90   5.352%   $242.2042   $242.20   $242.20   $242.20  
  Purchase #3 $146.26   11.704%   $163.3783   $163.38   $163.40   $163.40  
  Purchase #4 $244.34   7.200%   $261.9325   $261.93   $261.95   $261.90  
  Purchase #5 $65.55   9.443%   $71.7399   $71.74   $71.75   $71.70  
  Purchase #6 $188.66   3.382%   $195.0405   $195.04   $195.05   $195.00  
  Purchase #7 $5.93   5.447%   $6.253   $6.25   $6.25   $6.30  
  7 purchase totals = $948.97       $1,013.7558   $1,013.75   $1,013.80   $1,013.70