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 $61.54   13.278%   $69.7113   $69.71   $69.70   $69.70  
  Purchase #2 $33.51   3.305%   $34.6175   $34.62   $34.60   $34.60  
  Purchase #3 $61.67   5.210%   $64.883   $64.88   $64.90   $64.90  
  Purchase #4 $101.70   11.857%   $113.7586   $113.76   $113.75   $113.80  
  Purchase #5 $231.86   12.664%   $261.2228   $261.22   $261.20   $261.20  
  Purchase #6 $29.26   3.626%   $30.321   $30.32   $30.30   $30.30  
  Purchase #7 $131.29   9.150%   $143.303   $143.30   $143.30   $143.30  
  7 purchase totals = $650.83       $717.8172   $717.81   $717.75   $717.80