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 $230.97   13.422%   $261.9708   $261.97   $261.95   $262.00  
  Purchase #2 $212.41   4.153%   $221.2314   $221.23   $221.25   $221.20  
  Purchase #3 $154.43   4.857%   $161.9307   $161.93   $161.95   $161.90  
  Purchase #4 $71.49   11.536%   $79.7371   $79.74   $79.75   $79.70  
  Purchase #5 $182.42   9.105%   $199.0293   $199.03   $199.05   $199.00  
  Purchase #6 $72.96   7.299%   $78.2854   $78.29   $78.30   $78.30  
  Purchase #7 $121.73   8.218%   $131.7338   $131.73   $131.75   $131.70  
  7 purchase totals = $1,046.41       $1,133.9185   $1,133.92   $1,134.00   $1,133.80