Its best to consider Coinbase an institutional bank rather than an exchange. Your pricing for USD to BTC, ETH, or LTC is pre-determined at a fixed rate that is periodically updated.
Rather than use Coinbase, you will get a better rate if instead you convert USD to BTC via GDAX (the sister exchange to Coinbase) or Kracken if you are a US citizen. In addition these three exchanges can be used within Coinigy.
PS: Coinbase does not have API integration with Coinigy. This is likely because Coinbase does not offer an exchange market, but it's sister site GDAX does.