You're not going to get a good answer to your question because you've provided absolutely no information such as your VoIP provider, VoIP hardware and EFTPOS terminal type. The only real answer to your question is "possibly".
Your best solution is to ask your VoIP provider if they support EFTPOS.
EFTPOS can work fine fine VoIP but it depends entitely on your VoIP provider and your hardware. Some old terminals are very fussy about VoIP connections and will fail unless a low pass filter is fitted to the FXS port.
With 99% of new terminals supporting IP it's a moot point anyway, IP EFTPOS should be your solution, not VoIP.
*Need help configuring your Linksys ATA or IP Phones for New Zealand? Check my blog post