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 $50.61   10.698%   $56.0243   $56.02   $56.00   $56.00  
  Purchase #2 $97.85   8.659%   $106.3228   $106.32   $106.30   $106.30  
  Purchase #3 $116.75   13.274%   $132.2474   $132.25   $132.25   $132.20  
  Purchase #4 $117.82   3.232%   $121.6279   $121.63   $121.65   $121.60  
  Purchase #5 $9.99   8.734%   $10.8625   $10.86   $10.85   $10.90  
  Purchase #6 $236.36   3.491%   $244.6113   $244.61   $244.60   $244.60  
  Purchase #7 $170.82   4.159%   $177.9244   $177.92   $177.90   $177.90  
  7 purchase totals = $800.20       $849.6206   $849.61   $849.55   $849.50