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 $238.92   9.629%   $261.9256   $261.93   $261.95   $261.90  
  Purchase #2 $154.39   12.257%   $173.3136   $173.31   $173.30   $173.30  
  Purchase #3 $184.57   12.846%   $208.2799   $208.28   $208.30   $208.30  
  Purchase #4 $193.45   11.141%   $215.0023   $215.00   $215.00   $215.00  
  Purchase #5 $60.75   9.402%   $66.4617   $66.46   $66.45   $66.50  
  Purchase #6 $85.27   13.714%   $96.9639   $96.96   $96.95   $97.00  
  Purchase #7 $130.70   8.641%   $141.9938   $141.99   $142.00   $142.00  
  7 purchase totals = $1,048.05       $1,163.9408   $1,163.93   $1,163.95   $1,164.00