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 $236.83   12.276%   $265.9033   $265.90   $265.90   $265.90  
  Purchase #2 $163.82   11.178%   $182.1318   $182.13   $182.15   $182.10  
  Purchase #3 $90.53   12.192%   $101.5674   $101.57   $101.55   $101.60  
  Purchase #4 $46.62   12.376%   $52.3897   $52.39   $52.40   $52.40  
  Purchase #5 $135.30   3.469%   $139.9936   $139.99   $140.00   $140.00  
  Purchase #6 $72.86   5.640%   $76.9693   $76.97   $76.95   $77.00  
  Purchase #7 $226.57   10.534%   $250.4369   $250.44   $250.45   $250.40  
  7 purchase totals = $972.53       $1,069.3920   $1,069.39   $1,069.40   $1,069.40