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 $209.83   12.768%   $236.6211   $236.62   $236.60   $236.60  
  Purchase #2 $28.79   3.379%   $29.7628   $29.76   $29.75   $29.80  
  Purchase #3 $7.80   11.775%   $8.7185   $8.72   $8.70   $8.70  
  Purchase #4 $219.53   7.750%   $236.5436   $236.54   $236.55   $236.50  
  Purchase #5 $237.83   9.808%   $261.1564   $261.16   $261.15   $261.20  
  Purchase #6 $22.47   4.773%   $23.5425   $23.54   $23.55   $23.50  
  Purchase #7 $223.39   12.181%   $250.6011   $250.60   $250.60   $250.60  
  7 purchase totals = $949.64       $1,046.9460   $1,046.94   $1,046.90   $1,046.90