Sometimes the pot doesn't work out to an amount that can be split evenly. Traditionally, the high hand takes any excess amount.
In some games, it is necessary to "declare" whether you are going high or low simultaneously with the other players. In those cases, what works best is that a player has some identifiable object - a poker chip could be used but could get confused with the pot - which the player places in their hand if they wish to go high, or not if they wish to go low (of course, placing it or not in your hand should be a hidden task). Hands are outstretched over the table. Then all players at the declaration of the dealer show the contents of their hand. If they have the object, they are declaring high - if not, low. Some traditionalists drop the contents of the hand on the table. Not only does this get loud, but a hesitation by a player might allow them to change their mind and "palm" the object (which is why we don't invite prestidigitators...) and they also bounce around a lot making it difficult to tell who dropped what. Other ways can be devised to fairly and directly declare the players position. We typically would have the closed hands outstretched over the table, palms-up - and everyone must open their hand and reveal the object such that there is no question.
Some games allow for a person to declare that they are going to go for both high AND low simultaneously - for instance, a player in Seven Twenty Seven might have a 5 and two Aces, giving them both 7 and 27. In this case, they are allowed to "swing" the bet - that is, declare for both by having TWO objects in their hand. A person who swings a bet MUST win both high and low OUTRIGHT. If they lose or tie on either, they lose it all. Otherwise, everyone would do it...