It is absolutely correct to use two spaces following the end of a sentence, after the finishing punctuation mark (a period, exclamation point, or question mark).
The first time I ever saw it NOT done was in text put out by MS Word. I can't believe it caught on from there. It's just not proper!
BTW, DISUNC, two spaces follow U.S. postal zip code abbreviations, not five. Each state has a two-letter code to be typed in capital letters and followed by two spaces, then the zip code numbers. That's the proper form.