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 $232.33   13.202%   $263.0022   $263.00   $263.00   $263.00  
  Purchase #2 $35.92   8.397%   $38.9362   $38.94   $38.95   $38.90  
  Purchase #3 $58.42   12.448%   $65.6921   $65.69   $65.70   $65.70  
  Purchase #4 $154.94   4.520%   $161.9433   $161.94   $161.95   $161.90  
  Purchase #5 $166.76   4.131%   $173.6489   $173.65   $173.65   $173.60  
  Purchase #6 $109.86   4.340%   $114.6279   $114.63   $114.65   $114.60  
  Purchase #7 $207.59   10.546%   $229.4824   $229.48   $229.50   $229.50  
  7 purchase totals = $965.82       $1,047.3330   $1,047.33   $1,047.40   $1,047.20