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 $208.57   11.676%   $232.9226   $232.92   $232.90   $232.90  
  Purchase #2 $127.87   7.661%   $137.6661   $137.67   $137.65   $137.70  
  Purchase #3 $190.62   12.667%   $214.7658   $214.77   $214.75   $214.80  
  Purchase #4 $183.76   13.871%   $209.2493   $209.25   $209.25   $209.20  
  Purchase #5 $69.67   9.311%   $76.157   $76.16   $76.15   $76.20  
  Purchase #6 $38.27   10.179%   $42.1655   $42.17   $42.15   $42.20  
  Purchase #7 $45.76   4.208%   $47.6856   $47.69   $47.70   $47.70  
  7 purchase totals = $864.52       $960.6119   $960.63   $960.55   $960.70