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 $204.51   11.103%   $227.2167   $227.22   $227.20   $227.20  
  Purchase #2 $87.30   11.823%   $97.6215   $97.62   $97.60   $97.60  
  Purchase #3 $237.34   10.854%   $263.1009   $263.10   $263.10   $263.10  
  Purchase #4 $67.63   4.622%   $70.7559   $70.76   $70.75   $70.80  
  Purchase #5 $154.36   9.120%   $168.4376   $168.44   $168.45   $168.40  
  Purchase #6 $122.50   11.509%   $136.5985   $136.60   $136.60   $136.60  
  Purchase #7 $62.38   7.269%   $66.9144   $66.91   $66.90   $66.90  
  7 purchase totals = $936.02       $1,030.6455   $1,030.65   $1,030.60   $1,030.60