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 $124.82   13.430%   $141.5833   $141.58   $141.60   $141.60  
  Purchase #2 $221.90   12.643%   $249.9548   $249.95   $249.95   $250.00  
  Purchase #3 $207.37   10.638%   $229.43   $229.43   $229.45   $229.40  
  Purchase #4 $103.45   12.157%   $116.0264   $116.03   $116.05   $116.00  
  Purchase #5 $170.53   7.271%   $182.9292   $182.93   $182.95   $182.90  
  Purchase #6 $229.97   13.497%   $261.0091   $261.01   $261.00   $261.00  
  Purchase #7 $71.64   13.843%   $81.5571   $81.56   $81.55   $81.60  
  7 purchase totals = $1,129.68       $1,262.4899   $1,262.49   $1,262.55   $1,262.50