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 $42.94   10.760%   $47.5603   $47.56   $47.55   $47.60  
  Purchase #2 $76.50   4.787%   $80.1621   $80.16   $80.15   $80.20  
  Purchase #3 $31.38   4.166%   $32.6873   $32.69   $32.70   $32.70  
  Purchase #4 $46.45   9.655%   $50.9347   $50.93   $50.95   $50.90  
  Purchase #5 $97.75   4.267%   $101.921   $101.92   $101.90   $101.90  
  Purchase #6 $233.48   3.615%   $241.9203   $241.92   $241.90   $241.90  
  Purchase #7 $20.95   3.186%   $21.6175   $21.62   $21.60   $21.60  
  7 purchase totals = $549.45       $576.8032   $576.80   $576.75   $576.80