Thinking to sell a bit of my stash to help pay for unforeseen expense.

I've cashed out small amounts of like $20 long long ago with my Circle and Coinbase account. Might have to cash out a good bit more than that because of life event. Problem is is I've been dollar-cost-averaging using Bitwage for a long time so the Bitcoin I cash out comes from lots of transactions. I have no idea what the tax situation is or how I'd even calculate it. Anyone with similar experience cashing out a good bit of BTC to USD?

I keep a spreadsheet logging every BTC buy/sell I've ever made, with all details of the buy/sell like BTC/USD amounts, current and past values, date and time, etc.