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 $65.66   9.549%   $71.9299   $71.93   $71.95   $71.90  
  Purchase #2 $24.77   5.377%   $26.1019   $26.10   $26.10   $26.10  
  Purchase #3 $208.43   6.401%   $221.7716   $221.77   $221.75   $221.80  
  Purchase #4 $166.78   9.720%   $182.991   $182.99   $183.00   $183.00  
  Purchase #5 $115.57   6.866%   $123.505   $123.51   $123.50   $123.50  
  Purchase #6 $111.90   13.429%   $126.9271   $126.93   $126.95   $126.90  
  Purchase #7 $213.52   12.491%   $240.1908   $240.19   $240.20   $240.20  
  7 purchase totals = $906.63       $993.4173   $993.42   $993.45   $993.40