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 $237.44   13.613%   $269.7627   $269.76   $269.75   $269.80  
  Purchase #2 $56.46   6.760%   $60.2767   $60.28   $60.30   $60.30  
  Purchase #3 $173.77   10.703%   $192.3686   $192.37   $192.35   $192.40  
  Purchase #4 $24.94   5.652%   $26.3496   $26.35   $26.35   $26.30  
  Purchase #5 $56.41   13.192%   $63.8516   $63.85   $63.85   $63.90  
  Purchase #6 $107.58   8.499%   $116.7232   $116.72   $116.70   $116.70  
  Purchase #7 $35.93   11.476%   $40.0533   $40.05   $40.05   $40.10  
  7 purchase totals = $692.53       $769.3857   $769.38   $769.35   $769.50