I do the same thing (although you wouldn't catch me dead in a blazer). Before I worked t Target, I only held fast food jobs, so there was just the standardized ugly uniform, I had to wear my hair in a ponytail and under a stupid hat all day, and sweat all my makeup off. Now, even though I'm restricted to red and khaki, there's a lot more wiggle room and I like to make it look nice. I take pride in it...I generally take the time to curl my hair and wear something other than just a frumpy red t-shirt, and i wear cute shoes. Nobody has ever looked at me crazy for it, in fact I get lots of compliments on my hair. I have been asked by a lot of girls if my shoes hurt my feet (why yes, they do, but I don't let it show and I'm plenty efficient) but nobody has been rude about it. The only people that give me mean looks are the people who just generally don't like me anyway, I'm pretty sure it has nothing to do with the way I physically present myself.
If it makes you feel good to dress up then do so. But if it's not something you care for, then that's perfectly fine too. Whatever makes you feel comfortable in your skin is what you should go for. If others don't like what you're doing with yourself, they have an issue, not you. Don't change you to please someone else. That's ridiculous.