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 $239.39   9.136%   $261.2607   $261.26   $261.25   $261.30  
  Purchase #2 $92.74   13.722%   $105.4658   $105.47   $105.45   $105.50  
  Purchase #3 $103.74   10.116%   $114.2343   $114.23   $114.25   $114.20  
  Purchase #4 $58.95   7.119%   $63.1467   $63.15   $63.15   $63.10  
  Purchase #5 $172.53   4.838%   $180.877   $180.88   $180.90   $180.90  
  Purchase #6 $162.50   3.819%   $168.7059   $168.71   $168.70   $168.70  
  Purchase #7 $187.54   11.257%   $208.6514   $208.65   $208.65   $208.70  
  7 purchase totals = $1,017.39       $1,102.3418   $1,102.35   $1,102.35   $1,102.40