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 $52.38   9.202%   $57.2   $57.20   $57.20   $57.20  
  Purchase #2 $69.31   6.193%   $73.6024   $73.60   $73.60   $73.60  
  Purchase #3 $157.68   7.615%   $169.6873   $169.69   $169.70   $169.70  
  Purchase #4 $40.86   5.316%   $43.0321   $43.03   $43.05   $43.00  
  Purchase #5 $51.46   10.693%   $56.9626   $56.96   $56.95   $57.00  
  Purchase #6 $171.96   11.770%   $192.1997   $192.20   $192.20   $192.20  
  Purchase #7 $83.75   10.710%   $92.7196   $92.72   $92.70   $92.70  
  7 purchase totals = $627.40       $685.4037   $685.40   $685.40   $685.40