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 $10.46   9.771%   $11.482   $11.48   $11.50   $11.50  
  Purchase #2 $60.64   8.422%   $65.7471   $65.75   $65.75   $65.70  
  Purchase #3 $221.61   10.255%   $244.3361   $244.34   $244.35   $244.30  
  Purchase #4 $108.97   5.484%   $114.9459   $114.95   $114.95   $114.90  
  Purchase #5 $23.36   12.680%   $26.322   $26.32   $26.30   $26.30  
  Purchase #6 $151.83   13.726%   $172.6702   $172.67   $172.65   $172.70  
  Purchase #7 $234.86   6.610%   $250.3842   $250.38   $250.40   $250.40  
  7 purchase totals = $811.73       $885.8875   $885.89   $885.90   $885.80