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 $183.76   13.349%   $208.2901   $208.29   $208.30   $208.30  
  Purchase #2 $92.71   6.725%   $98.9447   $98.94   $98.95   $98.90  
  Purchase #3 $13.50   12.552%   $15.1945   $15.19   $15.20   $15.20  
  Purchase #4 $212.72   11.327%   $236.8148   $236.81   $236.80   $236.80  
  Purchase #5 $182.50   9.266%   $199.4105   $199.41   $199.40   $199.40  
  Purchase #6 $107.45   10.851%   $119.1094   $119.11   $119.10   $119.10  
  Purchase #7 $70.80   5.267%   $74.529   $74.53   $74.55   $74.50  
  7 purchase totals = $863.44       $952.2930   $952.28   $952.30   $952.20