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 $105.94   13.852%   $120.6148   $120.61   $120.60   $120.60  
  Purchase #2 $37.43   12.856%   $42.242   $42.24   $42.25   $42.20  
  Purchase #3 $67.73   9.291%   $74.0228   $74.02   $74.00   $74.00  
  Purchase #4 $247.38   5.688%   $261.451   $261.45   $261.45   $261.50  
  Purchase #5 $126.89   11.612%   $141.6245   $141.62   $141.60   $141.60  
  Purchase #6 $122.44   9.583%   $134.1734   $134.17   $134.15   $134.20  
  Purchase #7 $216.43   9.203%   $236.3481   $236.35   $236.35   $236.30  
  7 purchase totals = $924.24       $1,010.4766   $1,010.46   $1,010.40   $1,010.40