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 $44.93   5.228%   $47.2789   $47.28   $47.30   $47.30  
  Purchase #2 $159.83   10.104%   $175.9792   $175.98   $176.00   $176.00  
  Purchase #3 $245.77   6.447%   $261.6148   $261.61   $261.60   $261.60  
  Purchase #4 $165.75   3.773%   $172.0037   $172.00   $172.00   $172.00  
  Purchase #5 $129.50   10.649%   $143.2905   $143.29   $143.30   $143.30  
  Purchase #6 $13.63   13.744%   $15.5033   $15.50   $15.50   $15.50  
  Purchase #7 $84.50   10.485%   $93.3598   $93.36   $93.35   $93.40  
  7 purchase totals = $843.91       $909.0302   $909.02   $909.05   $909.10