No you can’t, if using different unit of measurement you need to setup an inventory item for each. It is better to use a POS for retail and restaurant businesses and use Manager for Accounting.
Which POS you recommend
No POS directly interfaces with Manager so you are free to choose any that fits your business. This Forum is about Manager and not promoting any other applications or POS systems. Other forums in your business segment are far more useful to recommend a POS.