Every retailer may add to the sales price:

1. (1) no amount on sales of ten cents or less;
2. (2) one cent on sales of eleven cents and over, but not in excess of twenty cents;
3. (3) two cents on sales of twenty-one cents and over, but not in excess of forty cents;
4. (4) three cents on sales of forty-one cents and over, but not in excess of sixty cents;
5. (5) four cents on sales of sixty-one cents and over, but not in excess of eighty cents;
6. (6) five cents on sales of eighty-one cents and over, but not in excess of one dollar;

7. (7) one cent additional for each twenty cents or major fraction thereon in excess of one dollar.

   The inability, impracticability, refusal, or failure to add these amounts to the sales price and collect from the purchaser does not relieve the taxpayer from the tax levied by this article.