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 $236.90   8.673%   $257.4463   $257.45   $257.45   $257.40  
  Purchase #2 $90.38   4.792%   $94.711   $94.71   $94.70   $94.70  
  Purchase #3 $220.45   9.697%   $241.827   $241.83   $241.85   $241.80  
  Purchase #4 $146.27   3.859%   $151.9146   $151.91   $151.90   $151.90  
  Purchase #5 $207.35   4.286%   $216.237   $216.24   $216.25   $216.20  
  Purchase #6 $114.90   9.649%   $125.9867   $125.99   $126.00   $126.00  
  Purchase #7 $144.42   5.583%   $152.483   $152.48   $152.50   $152.50  
  7 purchase totals = $1,160.67       $1,240.6056   $1,240.61   $1,240.65   $1,240.50