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 $208.94   9.411%   $228.6033   $228.60   $228.60   $228.60  
  Purchase #2 $150.75   11.223%   $167.6687   $167.67   $167.65   $167.70  
  Purchase #3 $35.44   10.342%   $39.1052   $39.11   $39.10   $39.10  
  Purchase #4 $52.99   13.716%   $60.2581   $60.26   $60.25   $60.30  
  Purchase #5 $182.34   5.673%   $192.6841   $192.68   $192.70   $192.70  
  Purchase #6 $90.46   8.237%   $97.9112   $97.91   $97.90   $97.90  
  Purchase #7 $67.51   4.584%   $70.6047   $70.60   $70.60   $70.60  
  7 purchase totals = $788.43       $856.8353   $856.83   $856.80   $856.90