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 $107.87   5.828%   $114.1567   $114.16   $114.15   $114.20  
  Purchase #2 $223.26   8.592%   $242.4425   $242.44   $242.45   $242.40  
  Purchase #3 $157.42   8.788%   $171.2541   $171.25   $171.25   $171.30  
  Purchase #4 $43.58   4.535%   $45.5564   $45.56   $45.55   $45.60  
  Purchase #5 $18.44   3.603%   $19.1044   $19.10   $19.10   $19.10  
  Purchase #6 $81.67   4.633%   $85.4538   $85.45   $85.45   $85.50  
  Purchase #7 $248.70   13.545%   $282.3864   $282.39   $282.40   $282.40  
  7 purchase totals = $880.94       $960.3543   $960.35   $960.35   $960.50