Was that cab I took the one where I went to that meeting across town? Was it the one I took home from the grocery store? No, wait. It was when - well, now I don't remember.
For tax purposes, and for personal sanity, it's a good idea to keep business transactions and personal ones separate. This is where you should consider maintaining a separate debit or credit account. Because when it comes time to review expenses, it's ideal to keep hair pulling to a minimum.
There are some expenses we don't want to relive, and going over the last 30 cups of coffee probably makes that category. Sure keeping one account for a while might work, but in the long run, keeping business expenses in a different account will save you from so many headaches.
Remember this: Opening up a separate account for business transactions will take the guesswork out of your payment history.