Will speaking Mandarin with crap tones cause communication difficulties?

I know to speak Mandarin perfectly, you need to master the tones, and that one word can have vastly different meanings depending on tone, often embarresingly different sometimes. However, will tone errors hinder communication, if you get the tone wrong, will people just have no idea what you’re asking, or …

What is the pinyin translation of this Mandarin sentence: 我可以购买一些你的皮肤药膏?

Either numbers or symbols for tones will do. My advisor at school (Traditional Chinese Medicine) makes the best stuff for acne & dermatitis- it just seems more appreciative to ask her for it in her native language. I only wish I could hear you say it, too. My pronunciation is …