I usually parked in Tai Po centre, you can validate with any receipts of $200 (any Tai po centre stores) with 1 hour free, and up to 2 hours free.
If you don't have things to spend in tai po centre, you can park in the mulit-level one next to Ocean Harbor restaurant, they have whole day parking for $30 in weekday, may be $10 per hour in weekend. I don't park there anymore as I will try to get 2 hours free parking always.
In Tai po market, the building with library should be cheaper ($5 per half hour), there are many parking with meters but not easy to find spots.