Aligning down to the pixel is very tricky as IMHO it's utterly impossible to try every possible browser currently in use (let alone the future ones). It's next to impossible to own -world-wide- all possible music players, pdas, phones, game consoles, tv set-top boxes, fridges, ...

Use a table or write a javascript snippet to add padding dynamically on load. For the javascript route - the key is to start with something too small, then increase it until you find that the list item height is half the list container height (i.e. it's jumped to two rows) - and then backtrack by one.