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 $208.66   3.637%   $216.249   $216.25   $216.25   $216.20  
  Purchase #2 $46.73   8.483%   $50.6941   $50.69   $50.70   $50.70  
  Purchase #3 $183.78   6.610%   $195.9279   $195.93   $195.95   $195.90  
  Purchase #4 $137.99   9.593%   $151.2274   $151.23   $151.25   $151.20  
  Purchase #5 $77.29   3.194%   $79.7586   $79.76   $79.75   $79.80  
  Purchase #6 $206.44   5.284%   $217.3483   $217.35   $217.35   $217.30  
  Purchase #7 $108.44   8.725%   $117.9014   $117.90   $117.90   $117.90  
  7 purchase totals = $969.33       $1,029.1067   $1,029.11   $1,029.15   $1,029.00