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 $218.84   9.529%   $239.6933   $239.69   $239.70   $239.70  
  Purchase #2 $183.55   6.327%   $195.1632   $195.16   $195.15   $195.20  
  Purchase #3 $231.94   12.641%   $261.2595   $261.26   $261.25   $261.30  
  Purchase #4 $240.99   5.684%   $254.6879   $254.69   $254.70   $254.70  
  Purchase #5 $5.94   9.536%   $6.5064   $6.51   $6.50   $6.50  
  Purchase #6 $40.56   4.170%   $42.2514   $42.25   $42.25   $42.30  
  Purchase #7 $218.45   13.752%   $248.4912   $248.49   $248.50   $248.50  
  7 purchase totals = $1,140.27       $1,248.0529   $1,248.05   $1,248.05   $1,248.20