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 $8.58   12.682%   $9.6681   $9.67   $9.65   $9.70  
  Purchase #2 $7.92   9.483%   $8.6711   $8.67   $8.65   $8.70  
  Purchase #3 $25.63   8.105%   $27.7073   $27.71   $27.70   $27.70  
  Purchase #4 $140.76   13.150%   $159.2699   $159.27   $159.25   $159.30  
  Purchase #5 $227.87   3.432%   $235.6905   $235.69   $235.70   $235.70  
  Purchase #6 $193.44   9.546%   $211.9058   $211.91   $211.90   $211.90  
  Purchase #7 $175.63   10.129%   $193.4196   $193.42   $193.40   $193.40  
  7 purchase totals = $779.83       $846.3323   $846.34   $846.25   $846.40