The words cashed, cached sound the same but have different meanings and spellings. Why do cashed, cached sound the same even though they are completely different words?
The answer is simple: cashed, cached are homophones of the English language.
Simple past tense and past participle of cache.
Having been cached.
Simple past tense and past participle of cash.
Exhausted or used up; finished, empty.
Definitions 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.