The words cashing, caching sound the same but have different meanings and spellings. Why do cashing, caching sound the same even though they are completely different words?
The answer is simple: cashing, caching are homophones of the English language.
Present participle of cache.
Present participle of cash.
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.