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 $249.26   7.193%   $267.1893   $267.19   $267.20   $267.20  
  Purchase #2 $242.29   11.242%   $269.5282   $269.53   $269.55   $269.50  
  Purchase #3 $186.83   11.727%   $208.7396   $208.74   $208.75   $208.70  
  Purchase #4 $105.97   8.202%   $114.6617   $114.66   $114.65   $114.70  
  Purchase #5 $77.69   9.250%   $84.8763   $84.88   $84.90   $84.90  
  Purchase #6 $114.56   13.469%   $129.9901   $129.99   $130.00   $130.00  
  Purchase #7 $162.34   4.614%   $169.8304   $169.83   $169.85   $169.80  
  7 purchase totals = $1,138.94       $1,244.8156   $1,244.82   $1,244.90   $1,244.80