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 $237.76   10.462%   $262.6345   $262.63   $262.65   $262.60  
  Purchase #2 $172.56   5.776%   $182.5271   $182.53   $182.55   $182.50  
  Purchase #3 $19.26   13.722%   $21.9029   $21.90   $21.90   $21.90  
  Purchase #4 $14.65   10.556%   $16.1965   $16.20   $16.20   $16.20  
  Purchase #5 $40.30   7.483%   $43.3156   $43.32   $43.30   $43.30  
  Purchase #6 $21.39   8.602%   $23.23   $23.23   $23.25   $23.20  
  Purchase #7 $218.79   6.214%   $232.3856   $232.39   $232.40   $232.40  
  7 purchase totals = $724.71       $782.1922   $782.20   $782.25   $782.10