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 $92.99   4.302%   $96.9904   $96.99   $97.00   $97.00  
  Purchase #2 $66.32   8.481%   $71.9446   $71.94   $71.95   $71.90  
  Purchase #3 $218.78   6.691%   $233.4186   $233.42   $233.40   $233.40  
  Purchase #4 $176.90   8.631%   $192.1682   $192.17   $192.15   $192.20  
  Purchase #5 $244.50   7.106%   $261.8742   $261.87   $261.85   $261.90  
  Purchase #6 $173.42   9.758%   $190.3423   $190.34   $190.35   $190.30  
  Purchase #7 $112.48   4.181%   $117.1828   $117.18   $117.20   $117.20  
  7 purchase totals = $1,085.39       $1,163.9211   $1,163.91   $1,163.90   $1,163.90