Advanced solution (true min)

public class MyClass {
    public static void main(String args[]) {
        int minCabRange = 0;
        int minBusRange = 20;
        int minTrainRange = 100;

        double baseCabTax = 0.70;
        double dayCabTaxPerKm = 0.79;
        double nightCabTaxPerKm = 0.90;

        double busTaxPerKm = 0.09;
        double trainTaxPerKm = 0.06;

        java.util.Scanner scanner = new java.util.Scanner(System.in);
        int kilometers = scanner.nextInt();
        String tariff = scanner.next();

        double priceForCab = 0.0;

        double priceForBus = 0.0;

        double priceForTrain = 0.0;

        if (tariff.equalsIgnoreCase("day")) {
            priceForCab = baseCabTax + kilometers * dayCabTaxPerKm;
        }
        if (tariff.equalsIgnoreCase("night")) {
            priceForCab = baseCabTax + kilometers * nightCabTaxPerKm;
        }

        priceForBus = kilometers * busTaxPerKm;

        priceForTrain = kilometers * trainTaxPerKm;
        double smallest = priceForCab;
        // >= 100km
        if (priceForTrain != 0 && kilometers > 100) {
            if(priceForTrain<priceForBus) {
                if(priceForCab<priceForTrain) {
                    smallest = priceForCab;
                } else {
                    smallest = priceForTrain;
                }
            } else {
                if(priceForBus<priceForCab) {
                    smallest = priceForBus;
                } else {
                    smallest = priceForCab;
                }
            }
        }
        // >= 20 && < 100
        if (priceForBus != 0 && (kilometers >= 20 && kilometers < 100)) {
            if (priceForCab > priceForBus) {
                smallest = priceForBus;
            }
            if (priceForCab < priceForBus) {
                smallest = priceForCab;
            }
            if (priceForBus == priceForCab) {
                smallest = priceForCab;
            }
        }

        System.out.printf("%.2f",smallest);
    }
}