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 $216.27   10.721%   $239.4563   $239.46   $239.45   $239.50  
  Purchase #2 $244.97   13.463%   $277.9503   $277.95   $277.95   $278.00  
  Purchase #3 $163.35   3.498%   $169.064   $169.06   $169.05   $169.10  
  Purchase #4 $224.42   6.434%   $238.8592   $238.86   $238.85   $238.90  
  Purchase #5 $36.64   9.605%   $40.1593   $40.16   $40.15   $40.20  
  Purchase #6 $15.78   4.428%   $16.4787   $16.48   $16.50   $16.50  
  Purchase #7 $199.92   13.361%   $226.6313   $226.63   $226.65   $226.60  
  7 purchase totals = $1,101.35       $1,208.5991   $1,208.60   $1,208.60   $1,208.80