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 $62.76   10.297%   $69.2224   $69.22   $69.20   $69.20  
  Purchase #2 $129.82   9.748%   $142.4749   $142.47   $142.45   $142.50  
  Purchase #3 $103.31   10.495%   $114.1524   $114.15   $114.15   $114.20  
  Purchase #4 $208.90   7.613%   $224.8036   $224.80   $224.80   $224.80  
  Purchase #5 $219.50   5.499%   $231.5703   $231.57   $231.55   $231.60  
  Purchase #6 $163.46   13.509%   $185.5418   $185.54   $185.55   $185.50  
  Purchase #7 $98.26   9.613%   $107.7057   $107.71   $107.70   $107.70  
  7 purchase totals = $986.01       $1,075.4711   $1,075.46   $1,075.40   $1,075.50