Using "salut" in the politeness preamble before the real interaction between a clerk and yourself is to be totally excluded, except, of course if you've become very friendly with a given clerk, and then again do not believe there is a necessity to abandon the standard formula "Bonjour" just because your relationship has become a friendly one, it is always a formula that sounds natural. There are several possibilities as to how might go the mutual introduction that is the point of the question.
One thing not to do is to submit yourself to a rigid routine of repeating blindly what a clerk might say to you in the way of greeting you or otherwise; to remain alert to what type of person is receiving you or taking care of your needs is a must and to remain free to take initiatives and to take them in opportune occasions is a good idea.
For instance, if you are a man and a clerk greets you with a simple "Monsieur…" don't repeat "Monsieur…": this is not exactly a greeting but rather a polite signal from the clerk that he is ready to consider your questions (similarly if you are a woman when a clerk says "Madame"). Here is another case when not to repeat what a clerk might say to you in the way of a greeting; there is a common enough usage to invert the words and you might hear from a clerk addressing you, if you are a man, "Monsieur, Bonjour"; it is a greeting in this case but the clerk's using it first makes it a rather personnal, idiosyncratic utterance of his and it is not of such a good inspiration to repeat it; a simple "Bonjour Monsieur" from your part will do, or even just "Bonjour".
The polite formula to use is basically "Bonjour"; it's the all purpose formula; first of all, it is the only formula to use with clerks that are no more than adolescents and who work in small shops; "Bonjour Madame" can be used for women, young or old, even though unmarried women are not called "madame" but "mademoiselle", but that type of uncontrollable error is never considered to matter really and no unmarried clerk to whom you've said "Bonjour madame" will ever point out to you that she should be addressed as "mademoiselle". Similarly, if a clerk is a young girl or a very young women you can add "mademoiselle" to your "Bonjour" (Bonjour mademoiselle).
The addition to your greetings of a "terme de civilité" or as it is said in English, of a title, makes them more refined, but I wouldn't say more polite; the question of choosing or not to be more refined is not an issue: the choice should insinuate itself naturally upon you, be felt as something to which you identify, and such states of mind, admittedly can be arrived at only out of exposure to life; to make a long story short, it is not necessary to put yourself through the routine of adding titles as long as you don't feel natural doing it.
There is no necessity to let cashiers be the first to say "Bonjour" to you, nor any other clerk; if you think about it first it's just as well to take the initiative.
In certain circumstances, for instance when you need to ask a clerk about something and that he is not attending to anyone, it is not even impolite to not pronounce any greetings; this is so, partly, for the reason that it is not quite proper to confer greetings to someone you don't know before having established eye contact; in such occasions it is accepted to address the person directly in a proper manner; for instance you may say "Monsieur! s'il vous plait.", ou "Madame? Vous vous occupez des clients", ou "Monsieur? un renseignement s'il vous plait.", etc.