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 $54.55   12.757%   $61.5089   $61.51   $61.50   $61.50  
  Purchase #2 $211.84   4.269%   $220.8834   $220.88   $220.90   $220.90  
  Purchase #3 $242.51   10.509%   $267.9954   $268.00   $268.00   $268.00  
  Purchase #4 $109.47   4.481%   $114.3754   $114.38   $114.40   $114.40  
  Purchase #5 $116.47   5.392%   $122.7501   $122.75   $122.75   $122.80  
  Purchase #6 $226.58   10.347%   $250.0242   $250.02   $250.00   $250.00  
  Purchase #7 $90.89   8.361%   $98.4893   $98.49   $98.50   $98.50  
  7 purchase totals = $1,052.31       $1,136.0267   $1,136.03   $1,136.05   $1,136.10