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 $58.84   13.713%   $66.9087   $66.91   $66.90   $66.90  
  Purchase #2 $101.60   12.581%   $114.3823   $114.38   $114.40   $114.40  
  Purchase #3 $105.58   8.367%   $114.4139   $114.41   $114.40   $114.40  
  Purchase #4 $111.46   11.604%   $124.3938   $124.39   $124.40   $124.40  
  Purchase #5 $97.50   12.836%   $110.0151   $110.02   $110.00   $110.00  
  Purchase #6 $70.55   9.367%   $77.1584   $77.16   $77.15   $77.20  
  Purchase #7 $217.84   5.831%   $230.5423   $230.54   $230.55   $230.50  
  7 purchase totals = $763.37       $837.8145   $837.81   $837.80   $837.80