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 $69.86   9.744%   $76.6672   $76.67   $76.65   $76.70  
  Purchase #2 $237.68   6.154%   $252.3068   $252.31   $252.30   $252.30  
  Purchase #3 $39.67   9.752%   $43.5386   $43.54   $43.55   $43.50  
  Purchase #4 $47.89   11.860%   $53.5698   $53.57   $53.55   $53.60  
  Purchase #5 $154.98   13.274%   $175.552   $175.55   $175.55   $175.60  
  Purchase #6 $146.38   8.361%   $158.6188   $158.62   $158.60   $158.60  
  Purchase #7 $199.83   8.712%   $217.2392   $217.24   $217.25   $217.20  
  7 purchase totals = $896.29       $977.4924   $977.50   $977.45   $977.50