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 $62.67   5.235%   $65.9508   $65.95   $65.95   $66.00  
  Purchase #2 $153.58   10.396%   $169.5462   $169.55   $169.55   $169.50  
  Purchase #3 $56.45   8.782%   $61.4074   $61.41   $61.40   $61.40  
  Purchase #4 $101.66   12.211%   $114.0737   $114.07   $114.05   $114.10  
  Purchase #5 $128.76   5.597%   $135.9667   $135.97   $135.95   $136.00  
  Purchase #6 $76.48   13.593%   $86.8759   $86.88   $86.90   $86.90  
  Purchase #7 $52.90   11.374%   $58.9168   $58.92   $58.90   $58.90  
  7 purchase totals = $632.50       $692.7375   $692.75   $692.70   $692.80