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 $60.42   10.163%   $66.5605   $66.56   $66.55   $66.60  
  Purchase #2 $167.38   3.706%   $173.5831   $173.58   $173.60   $173.60  
  Purchase #3 $70.38   3.744%   $73.015   $73.02   $73.00   $73.00  
  Purchase #4 $53.47   8.812%   $58.1818   $58.18   $58.20   $58.20  
  Purchase #5 $51.41   4.750%   $53.852   $53.85   $53.85   $53.90  
  Purchase #6 $68.84   3.509%   $71.2556   $71.26   $71.25   $71.30  
  Purchase #7 $151.59   13.304%   $171.7575   $171.76   $171.75   $171.80  
  7 purchase totals = $623.49       $668.2055   $668.21   $668.20   $668.40