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 $240.28   8.730%   $261.2564   $261.26   $261.25   $261.30  
  Purchase #2 $61.92   13.317%   $70.1659   $70.17   $70.15   $70.20  
  Purchase #3 $233.61   11.229%   $259.8421   $259.84   $259.85   $259.80  
  Purchase #4 $60.96   8.116%   $65.9075   $65.91   $65.90   $65.90  
  Purchase #5 $237.83   3.357%   $245.814   $245.81   $245.80   $245.80  
  Purchase #6 $117.90   5.793%   $124.7299   $124.73   $124.75   $124.70  
  Purchase #7 $79.99   5.622%   $84.487   $84.49   $84.50   $84.50  
  7 purchase totals = $1,032.49       $1,112.2028   $1,112.21   $1,112.20   $1,112.20