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 $208.74   13.359%   $236.6256   $236.63   $236.65   $236.60  
  Purchase #2 $205.42   4.200%   $214.0476   $214.05   $214.05   $214.00  
  Purchase #3 $47.76   6.675%   $50.948   $50.95   $50.95   $50.90  
  Purchase #4 $94.94   3.130%   $97.9116   $97.91   $97.90   $97.90  
  Purchase #5 $34.27   3.447%   $35.4513   $35.45   $35.45   $35.50  
  Purchase #6 $70.82   10.605%   $78.3305   $78.33   $78.35   $78.30  
  Purchase #7 $7.82   11.758%   $8.7395   $8.74   $8.75   $8.70  
  7 purchase totals = $669.77       $722.0541   $722.06   $722.10   $721.90