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 $169.41   7.784%   $182.5969   $182.60   $182.60   $182.60  
  Purchase #2 $41.69   11.302%   $46.4018   $46.40   $46.40   $46.40  
  Purchase #3 $19.32   3.471%   $19.9906   $19.99   $20.00   $20.00  
  Purchase #4 $43.36   12.406%   $48.7392   $48.74   $48.75   $48.70  
  Purchase #5 $214.61   11.617%   $239.5412   $239.54   $239.55   $239.50  
  Purchase #6 $60.39   8.312%   $65.4096   $65.41   $65.40   $65.40  
  Purchase #7 $68.81   10.288%   $75.8892   $75.89   $75.90   $75.90  
  7 purchase totals = $617.59       $678.5685   $678.57   $678.60   $678.50