I worked at a small hardware store for 10 years and we had a similar price structure. For low cost items (under $5 cost) the markup target was about 100%, so a $3.00 cost item would sell for $5.99. In the business world you use a different formula so the percentages don't get as crazy. We calculated Gross Profit Margin which gives a percentage between 0 and 100. Formula was 1 - Cost/Retail, then multiply by 100 to change it from a decimal to a percentage. So if an item sold for 100% more than cost, it had a GPM of 50%, and 200% more than cost had a GPM of 66%.
And Ideally for Items below $20, you'd aim for 50-60% GPM. More expensive items (over $100) had worse margins (sometimes only 5-10% GPM) because people compare prices more when buying those items.
So the tldr version is: 100% markup is not uncommon for low cost items in the retail world.