let products = [
  { "produkt": "Joghurt", "preis": 2.49 },
  { "produkt": "Brot",    "preis": 3.29 },
  { "produkt": "Käse",    "preis": 8.99 },
  { "produkt": "Duschgel","preis": 2.79 }
]

let reduced_products = []
const discound_and_round = price => Math.floor(price*0.9*10**2+0.5)/10**2 //price*0.9.toFixed(2) is not working!

for(product of products){
    const new_product = new Map()

    new_product.set("produkt",product.produkt)
    new_product.set("preis", discound_and_round(product.preis)) 

    reduced_products.push(new_product)
}

console.log("Normale Preise:")
for(product of products){
    console.log(product)
}

console.log("\n")

console.log("Reduzierte Preise:")
for(product of reduced_products){
    console.log(product)
}