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 $38.67   12.564%   $43.5285   $43.53   $43.55   $43.50  
  Purchase #2 $162.68   9.762%   $178.5608   $178.56   $178.55   $178.60  
  Purchase #3 $73.94   3.575%   $76.5834   $76.58   $76.60   $76.60  
  Purchase #4 $27.65   11.708%   $30.8873   $30.89   $30.90   $30.90  
  Purchase #5 $44.40   5.237%   $46.7252   $46.73   $46.75   $46.70  
  Purchase #6 $135.66   13.188%   $153.5508   $153.55   $153.55   $153.60  
  Purchase #7 $214.94   9.441%   $235.2325   $235.23   $235.25   $235.20  
  7 purchase totals = $697.94       $765.0685   $765.07   $765.15   $765.10