Back in June, my colleague Walt Frick reported that mobile advertising company Nexage had raised $10 million in series B funding. The investment came largely from SingTel Innov8 (the corporate venture capital arm of the SingTel Group), Relay Ventures, and GrandBanks Capital. Nexage, however, isn’t done raising funds. They announced today that they’ve secured an additional $5 million from Hearst Interactive Media to close the Series B.

Even with the extra cash lining their deep pockets, Nexage won’t stray from the course they’ve already set. According to Ernie Cormier, CEO and president of Nexage in the press release, “Our mission remains the same with this additional Series B funding: to extend our RTB leadership, champion and support the needs of our premium customers, and accelerate the maturity of the mobile advertising market.”

Nexage is a pioneer in mobile advertising, championing the idea of real-time bidding (RTB) by helping to open industry standards for communication between buyers of advertising and sellers of publisher inventory. The latest funding will help to bolster Nexage’s presence in the predicted $20.6 billion mobile advertising market by 2015; RTB is expected to constitute roughly 30% of that market.

Such a productive player in a fruitful market is something that Hearst Interactive VP Darcy Frisch is hoping to take advantage of. “We are thrilled about this opportunity to invest in Nexage, helping it shape and expand a market that has become increasingly vital for publishers and advertisers alike,” said Frisch, who will join Nexage’s board of directors.

With the latest addition to their series B, Nexage has raised a total of $19.5 million in venture capital. They are headquartered in Waltham, MA.