mainehiker...
I do not trade NEM, so this is just a general observation. NEM could easily traded above your asking price without your being filled - there are no guarantees of that. The usual cause of that for NYSE listed stocks is the size rule, where size takes precedence over price. If you are offering 1000 shares at $29.50 and an order comes in to purchase 10,000 shares at $30, the specialist is under no obligation to fill your order if he has a willing seller who will accommodate the whole 10,000 shares at $30. There are other possibilities, such as under the same rule, the specialist himself could sell the 10,000 shares at $30 (but not at 29.50) or it could have been an "off exchange" trade at the Philly exchange, for instance, or a NAZDAQ or Island trade.
Such rules are also how you frequently see "outside" trades, either above the ask price or below the bid price. Had your order been for a NAZ stock, the fact that there are many market makers could also enter into it.
Hope that helps.
mlsoft