Second-half property tax bills showing up soon in your mailbox will rise on average only 1 to 2 percent from last year but, given declining home values, the real hit will be a lot bigger.  Because of the lingering effect of the subprime-mortgage recession, property values are still slipping.  That means that, with government still asking for more revenue, property tax rates are up — 6.8 percent in the city and an average of 12 to 19 percent in the suburban areas of the county.