PosInitial.scala

case class Pricing(val quantity: Int, val unitPrice: UnitPrice, val tierPrice: TierPrice)

case class UnitPrice(val price: BigDecimal)

case class TierPrice(val price: BigDecimal, val quantity: Int)

def total(croissants: Pricing, baguettes: Pricing): BigDecimal = {
  val croissantTotal = total(croissants)
  val baguetteTotal = total(baguettes)

  croissantTotal + baguetteTotal
}

private def total(pricing: Pricing): BigDecimal = {
  val tiers = pricing.quantity / pricing.tierPrice.quantity
  val regularPricedArticles = pricing.quantity % pricing.tierPrice.quantity
  tiers * pricing.tierPrice.price + regularPricedArticles * pricing.unitPrice.price
}