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 $211.95   10.380%   $233.9504   $233.95   $233.95   $234.00  
  Purchase #2 $101.62   12.552%   $114.3753   $114.38   $114.40   $114.40  
  Purchase #3 $235.32   7.619%   $253.249   $253.25   $253.25   $253.20  
  Purchase #4 $190.59   4.110%   $198.4232   $198.42   $198.40   $198.40  
  Purchase #5 $164.50   7.237%   $176.4049   $176.40   $176.40   $176.40  
  Purchase #6 $42.74   5.401%   $45.0484   $45.05   $45.05   $45.00  
  Purchase #7 $18.35   3.826%   $19.0521   $19.05   $19.05   $19.10  
  7 purchase totals = $965.07       $1,040.5033   $1,040.50   $1,040.50   $1,040.50