var peopleAmount = [0,0,0,0,0,0,0,0,0];

function makeList(calculation) {
	for(i=0; i<peopleAmount.length; i++) {
		if(calculation >200 && calculation < 300) {
			peopleAmount[0] += 1;
		}
		else if(calculation > 300 && calculation < 400) {
			peopleAmount[1] += 1;
		}
		....so on and so forth
	}
}

function calculate() {
	var salesAmount = document.getElementById("salesAmount");
    var salesAmount = parseInt(salesAmount.value);
    var calculation = salesAmount *.09;
    var calculation = calculation + 200;

	makeList(calculation);
}