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 $23.76   4.806%   $24.9019   $24.90   $24.90   $24.90  
  Purchase #2 $196.80   8.457%   $213.4434   $213.44   $213.45   $213.40  
  Purchase #3 $149.38   3.430%   $154.5037   $154.50   $154.50   $154.50  
  Purchase #4 $11.84   12.125%   $13.2756   $13.28   $13.30   $13.30  
  Purchase #5 $60.83   9.510%   $66.6149   $66.61   $66.60   $66.60  
  Purchase #6 $183.56   5.128%   $192.973   $192.97   $192.95   $193.00  
  Purchase #7 $229.48   12.479%   $258.1168   $258.12   $258.10   $258.10  
  7 purchase totals = $855.65       $923.8293   $923.82   $923.80   $923.80