If you hire an electrician to wire your house, he doesn't say “This costs $3,500 (or whatever) and another $700 to ground everything properly." He says "That will cost $4,200", because he is a professional, and he is going to do the job correctly, or not at all.

Part of our jobs as professional developers is to understand the potential business impact on a feature and not invest time on documentation or unit tests for code that will probably be dropped next week. That said, and not to be harsh—but if you want to be treated like a professional, act like one, and set expectations for how much a feature costs to deliver, rather than breaking your work down into separate tasks and inviting your supervisor to discard the tasks he doesn't understand.