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 $241.25   11.543%   $269.0975   $269.10   $269.10   $269.10  
  Purchase #2 $51.58   7.397%   $55.3954   $55.40   $55.40   $55.40  
  Purchase #3 $214.92   3.615%   $222.6894   $222.69   $222.70   $222.70  
  Purchase #4 $107.61   10.797%   $119.2287   $119.23   $119.25   $119.20  
  Purchase #5 $107.80   4.210%   $112.3384   $112.34   $112.35   $112.30  
  Purchase #6 $114.25   13.821%   $130.0405   $130.04   $130.05   $130.00  
  Purchase #7 $197.96   5.863%   $209.5664   $209.57   $209.55   $209.60  
  7 purchase totals = $1,035.37       $1,118.3563   $1,118.37   $1,118.40   $1,118.30