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 $178.29   8.211%   $192.9294   $192.93   $192.95   $192.90  
  Purchase #2 $122.81   5.819%   $129.9563   $129.96   $129.95   $130.00  
  Purchase #3 $188.39   5.282%   $198.3408   $198.34   $198.35   $198.30  
  Purchase #4 $101.95   12.182%   $114.3695   $114.37   $114.35   $114.40  
  Purchase #5 $107.44   8.243%   $116.2963   $116.30   $116.30   $116.30  
  Purchase #6 $248.91   11.788%   $278.2515   $278.25   $278.25   $278.30  
  Purchase #7 $217.64   9.126%   $237.5018   $237.50   $237.50   $237.50  
  7 purchase totals = $1,165.43       $1,267.6456   $1,267.65   $1,267.65   $1,267.70