Triathlon Cycling Shoes

In terms of sizing regarding the Tri shoe for the bike, I was wondering if it would be best to go slightly bigger than your normal shoe size. Where I am located availability for shoes is very limited and they need to be ordered. I understand that its down to personal preference and probably the brand. My last pair were Giro and I chose the same size as I my regular walking shoes, i found at times they can irritate the end of the toes. i was thinking to increase by just .5, but unsure if this is the correct thing to do