Run a stopwatch on real work, round it the way your contracts do, and turn the week into a CSV or a printable invoice-ready timesheet. Toggl, Harvest and Hubstaff charge per seat per month and hold your data on their servers; this keeps it in your browser, works with the tab closed, and exports to a spreadsheet any accountant can open. No seat to buy, no cloud, no tracking of you while you track your time.
Entries are kept in this browser's local storage. That means the stopwatch keeps running while the tab is shut and the phone is in your pocket, because only the start time is stored and the elapsed figure is recalculated from the clock — but it also means the data lives on this one device and this one browser. Clearing site data deletes it, so export a CSV before you clear anything, and treat the export as your real record.
Rounding is applied per entry, not to the day's total, which is how most agencies bill: six minutes is a tenth of an hour, so "nearest 6" is the same as billing in tenths. A seven-minute call rounds to six, a nine-minute one to twelve. The exact figure is always kept underneath, so switching back to "exact minutes" loses nothing.
The printable timesheet is a plain HTML table with the project, date, description, rounded hours and rate — the format most finance teams expect, and something you can paste into an invoice without re-typing.