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 $22.63   4.244%   $23.5904   $23.59   $23.60   $23.60  
  Purchase #2 $60.69   13.571%   $68.9262   $68.93   $68.95   $68.90  
  Purchase #3 $176.65   9.251%   $192.9919   $192.99   $193.00   $193.00  
  Purchase #4 $232.46   8.543%   $252.3191   $252.32   $252.30   $252.30  
  Purchase #5 $9.92   11.179%   $11.029   $11.03   $11.05   $11.00  
  Purchase #6 $75.86   9.391%   $82.984   $82.98   $83.00   $83.00  
  Purchase #7 $190.86   9.376%   $208.755   $208.76   $208.75   $208.80  
  7 purchase totals = $769.07       $840.5956   $840.60   $840.65   $840.60