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 $215.60   12.127%   $241.7458   $241.75   $241.75   $241.70  
  Purchase #2 $141.41   12.227%   $158.7002   $158.70   $158.70   $158.70  
  Purchase #3 $12.59   8.266%   $13.6307   $13.63   $13.65   $13.60  
  Purchase #4 $101.40   5.779%   $107.2599   $107.26   $107.25   $107.30  
  Purchase #5 $234.62   13.412%   $266.0872   $266.09   $266.10   $266.10  
  Purchase #6 $117.46   8.292%   $127.1998   $127.20   $127.20   $127.20  
  Purchase #7 $8.61   3.745%   $8.9324   $8.93   $8.95   $8.90  
  7 purchase totals = $831.69       $923.5560   $923.56   $923.60   $923.50