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 $226.69   3.486%   $234.5924   $234.59   $234.60   $234.60  
  Purchase #2 $50.46   11.195%   $56.109   $56.11   $56.10   $56.10  
  Purchase #3 $239.44   9.105%   $261.241   $261.24   $261.25   $261.20  
  Purchase #4 $196.92   12.573%   $221.6788   $221.68   $221.70   $221.70  
  Purchase #5 $173.33   7.282%   $185.9519   $185.95   $185.95   $186.00  
  Purchase #6 $236.74   13.809%   $269.4314   $269.43   $269.45   $269.40  
  Purchase #7 $132.37   6.349%   $140.7742   $140.77   $140.75   $140.80  
  7 purchase totals = $1,255.95       $1,369.7787   $1,369.77   $1,369.80   $1,369.80