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 $21.25   5.634%   $22.4472   $22.45   $22.45   $22.40  
  Purchase #2 $76.42   10.110%   $84.1461   $84.15   $84.15   $84.10  
  Purchase #3 $34.78   8.773%   $37.8312   $37.83   $37.85   $37.80  
  Purchase #4 $38.92   3.213%   $40.1705   $40.17   $40.15   $40.20  
  Purchase #5 $14.69   12.597%   $16.5405   $16.54   $16.55   $16.50  
  Purchase #6 $69.81   13.483%   $79.2225   $79.22   $79.20   $79.20  
  Purchase #7 $110.58   3.498%   $114.4481   $114.45   $114.45   $114.40  
  7 purchase totals = $366.45       $394.8061   $394.81   $394.80   $394.60