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 $57.34   8.854%   $62.4169   $62.42   $62.40   $62.40  
  Purchase #2 $197.25   12.134%   $221.1843   $221.18   $221.20   $221.20  
  Purchase #3 $106.63   10.407%   $117.727   $117.73   $117.75   $117.70  
  Purchase #4 $244.92   7.235%   $262.64   $262.64   $262.65   $262.60  
  Purchase #5 $117.79   10.538%   $130.2027   $130.20   $130.20   $130.20  
  Purchase #6 $44.66   6.662%   $47.6352   $47.64   $47.65   $47.60  
  Purchase #7 $60.93   10.292%   $67.2009   $67.20   $67.20   $67.20  
  7 purchase totals = $829.52       $909.0070   $909.01   $909.05   $908.90