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 $249.67   10.527%   $275.9528   $275.95   $275.95   $276.00  
  Purchase #2 $197.99   8.848%   $215.5082   $215.51   $215.50   $215.50  
  Purchase #3 $162.75   12.314%   $182.791   $182.79   $182.80   $182.80  
  Purchase #4 $245.48   9.735%   $269.3775   $269.38   $269.40   $269.40  
  Purchase #5 $130.51   5.303%   $137.4309   $137.43   $137.45   $137.40  
  Purchase #6 $73.51   12.178%   $82.462   $82.46   $82.45   $82.50  
  Purchase #7 $248.77   8.607%   $270.1816   $270.18   $270.20   $270.20  
  7 purchase totals = $1,308.68       $1,433.7040   $1,433.70   $1,433.75   $1,433.80