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 $56.88   3.598%   $58.9265   $58.93   $58.95   $58.90  
  Purchase #2 $233.58   6.160%   $247.9685   $247.97   $247.95   $248.00  
  Purchase #3 $108.60   5.405%   $114.4698   $114.47   $114.45   $114.50  
  Purchase #4 $218.79   10.566%   $241.9074   $241.91   $241.90   $241.90  
  Purchase #5 $124.92   12.540%   $140.585   $140.59   $140.60   $140.60  
  Purchase #6 $157.56   4.570%   $164.7605   $164.76   $164.75   $164.80  
  Purchase #7 $68.70   8.763%   $74.7202   $74.72   $74.70   $74.70  
  7 purchase totals = $969.03       $1,043.3379   $1,043.35   $1,043.30   $1,043.40