You have likely heard about the exhaustion of available IPv4 addresses and the push to adopt IPv6. IP addresses have a maximum number of possibilities, and to help minimize the unnecessary usage of remaining IP addresses, web hosting providers offer virtual name-based hosting on shared hosting accounts rather than dedicated IP hosting. They make an exception, however, for e-commerce customers, and there is a very good reason why.
Whether you are using web applications for CRM (customer relationship management), POS (point of sale), or for an e-commerce storefront and shopping cart, you will probably want to make sure transactions, logins, and the collection of user data is secure. Unless you are using a third-party e-commerce provider to handle transactions, the best way to make sure they are secure is to use SSL (Secure Sockets Layer) or TLS (Transport Layer Security). With this security technology, your customers will connect to your site via secure HTTPS rather than plain HTTP.
In order to function properly, SSL requires a dedicated IP address, and many web hosts will offer special packages for e-commerce users who need them. You will also need an SSL certificate, which user agents (web browsers) will use to validate the authenticity of your secure transaction. Anytime a customer initiates a transaction on your secure site, the information exchange will be encrypted and safe from prying eyes.
Is it possible to have an e-commerce site without a dedicated IP address? It certainly is, but not having SSL will prevent you from being able to offer customers a secure shopping interface directly on your site. With customers you want to build a trusting relationship, and for that, you will probably need a dedicated IP.