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 $248.41   8.613%   $269.8056   $269.81   $269.80   $269.80  
  Purchase #2 $113.59   4.404%   $118.5925   $118.59   $118.60   $118.60  
  Purchase #3 $231.52   8.189%   $250.4792   $250.48   $250.50   $250.50  
  Purchase #4 $57.52   13.351%   $65.1995   $65.20   $65.20   $65.20  
  Purchase #5 $176.27   12.674%   $198.6105   $198.61   $198.60   $198.60  
  Purchase #6 $114.84   13.396%   $130.224   $130.22   $130.20   $130.20  
  Purchase #7 $125.55   4.401%   $131.0755   $131.08   $131.10   $131.10  
  7 purchase totals = $1,067.70       $1,163.9868   $1,163.99   $1,164.00   $1,164.00