Maths Type Question

Riddle: There is a shop that reads: Buy 1 for $1.00 10 for $2.00 100 for $3.00 I needed 913 and still only paid $3.00. How could this be financially viable for the shop-keeper?

Answer: They are numbers for houses and it's $1 per digit. Source: https://riddles.com/6246

There is a shop that reads: Buy 1 for $1.00 10 for $2.00 100 for $3.00 I needed 913 and still only paid $3.00. How could this be financially viable for the shop-keeper? — Maths type question by Lakshmanan Riddle