In the UK, income tax is only calculated on whole pounds earned. Thus it's not possible to have a tax amount due which is not in whole pence. (And the rounding is in your favour - so an annual salary of £50,000.99 is taxed as if you just received £50,000.00.)
As MT says, the approach used for most of us wage slaves is a cumulative calculation, whereby each month the payroll system calculates how much tax you should have paid in total so far this tax year, and deducts how much you've already paid, and thus gets how much you pay this month/week.
Your tax allowances as indicated by your tax code are also apportioned over the year, so the month 7 calculation, for example, will be performed allowing you 7/12ths of your total allowances (both for earnings before being taxed, but also for the amount you can earn at the lower tax rates). This has the effect of making your tax payments equal over the year if your earnings are constant over the year.
If you're on a Month 1 or Week 1 basis, this cumulative calculation doesn't apply, and each pay packet is taxed as if this is the first week/month of the tax year.