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 $246.38   9.428%   $269.6087   $269.61   $269.60   $269.60  
  Purchase #2 $42.76   9.441%   $46.797   $46.80   $46.80   $46.80  
  Purchase #3 $18.78   8.629%   $20.4005   $20.40   $20.40   $20.40  
  Purchase #4 $139.99   9.734%   $153.6166   $153.62   $153.60   $153.60  
  Purchase #5 $53.78   8.769%   $58.496   $58.50   $58.50   $58.50  
  Purchase #6 $152.92   10.110%   $168.3802   $168.38   $168.40   $168.40  
  Purchase #7 $105.59   8.661%   $114.7351   $114.74   $114.75   $114.70  
  7 purchase totals = $760.20       $832.0341   $832.05   $832.05   $832.00