The words tide, tied sound the same but have different meanings and spellings. Why do tide, tied sound the same even though they are completely different words?
The answer is simple: tide, tied are homophones of the English language.
The periodic variation in the surface level of the oceans and of bays, gulfs, inlets, and estuaries, caused by gravitational attraction of the moon and sun.
A specific occurrence of such a variation: awaiting the next high tide.
That resulted in a tie.
Simple past tense and past participle of tie.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").