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 $239.99   9.317%   $262.3499   $262.35   $262.35   $262.30  
  Purchase #2 $95.63   6.607%   $101.9483   $101.95   $101.95   $101.90  
  Purchase #3 $64.58   8.320%   $69.9531   $69.95   $69.95   $70.00  
  Purchase #4 $231.95   3.230%   $239.442   $239.44   $239.45   $239.40  
  Purchase #5 $119.29   7.790%   $128.5827   $128.58   $128.60   $128.60  
  Purchase #6 $174.73   12.263%   $196.1571   $196.16   $196.15   $196.20  
  Purchase #7 $240.80   8.483%   $261.2271   $261.23   $261.25   $261.20  
  7 purchase totals = $1,166.97       $1,259.6602   $1,259.66   $1,259.70   $1,259.60