The research has found that customers commonly associate prices ending in zeros as conveying a quality, premium message.
Prices ending in 9 are commonly associated with discounted, on sale, cheap.
Most customers know that $29 = $30.
When the time comes to increase a $29 price point, there is typically a drop in sales (albeit temporary, unless you've hit the customers price ceiling). You are less likely to experience that when increasing a $30 price point
Happy to chat further on this if you're interested