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 $247.93   11.760%   $277.0866   $277.09   $277.10   $277.10  
  Purchase #2 $109.81   3.305%   $113.4392   $113.44   $113.45   $113.40  
  Purchase #3 $125.45   7.303%   $134.6116   $134.61   $134.60   $134.60  
  Purchase #4 $248.74   5.692%   $262.8983   $262.90   $262.90   $262.90  
  Purchase #5 $223.42   7.175%   $239.4504   $239.45   $239.45   $239.50  
  Purchase #6 $102.39   13.566%   $116.2802   $116.28   $116.30   $116.30  
  Purchase #7 $58.83   3.599%   $60.9473   $60.95   $60.95   $60.90  
  7 purchase totals = $1,116.57       $1,204.7136   $1,204.72   $1,204.75   $1,204.70