Rather - you should be asking the question, why don’t the shops in the Netherlands, just mark up the price, to €1 instead?! Seems incredibly stupid, to me.
Shops worldwide do this; whether it is $1.99, €1,99, £1.99 or ¥499. It's a psychological trick. The exceptions (like the Dutch HEMA for which whole unit prices are part of its heritage) use it as a distinguishing feature, but most shops don't dare to.
Rather - you should be asking the question, why don’t the shops in the Netherlands, just mark up the price, to €1 instead?! Seems incredibly stupid, to me.