^ as above, depends where you live. I would be laughed down the garden path if quoted 10. 5 BUNGALOW windows and 2 doors. I'd be looking at about 7 or 8 quid.
And if they then tell their neighbour what a good job you did for 8 quid, you end up getting that too. So you'll be cleaning 16 quids work, whilst someone else has quoted 12, may have got it, but loses out whilst driving to next job.
IMO, little and often is best! The main thing, as posted already, is that you're happy with prices of your work.
The trick is, quote, 9s and 14s and 19s etc. 9/10 customers will always say, keep the change! When this happens 4 or 5 times a day, it'll soon add up through week!