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 $55.49   11.177%   $61.6921   $61.69   $61.70   $61.70  
  Purchase #2 $105.85   8.307%   $114.643   $114.64   $114.65   $114.60  
  Purchase #3 $104.64   9.468%   $114.5473   $114.55   $114.55   $114.50  
  Purchase #4 $67.55   10.392%   $74.5698   $74.57   $74.55   $74.60  
  Purchase #5 $93.46   3.361%   $96.6012   $96.60   $96.60   $96.60  
  Purchase #6 $182.33   5.798%   $192.9015   $192.90   $192.90   $192.90  
  Purchase #7 $236.34   5.162%   $248.5399   $248.54   $248.55   $248.50  
  7 purchase totals = $845.66       $903.4948   $903.49   $903.50   $903.40