The answers so far provide you some good insight as to why you might want to prefer cash CHF vs cash EUR. Allow me to add my view on avoiding this altogether.
If you are only travelling temporary and you use cash, they you always have some loss as you can'd budget to the nearest centime. You'll end up leaving with some cash CHF which you cannot use elsewhere and you'll probably keep it as "souvenirs".
I suggest that you take into account using a multi-currency card, like TransferWise*. This way you can keep an amount of USD in your account and the conversion is made every time you pay with it in CHF, at the mid-market rate. This way, you avoid converting too much or too little, and, more importantly, you avoid the unfair conversion rate of the shops and banks**.
As noted by a comment, most credit cards work this way. However, with the credit card of your bank, the conversion is done by them, at a rate that's advantageous for the bank, plus some non-negligible fee. With multi-currency cards, the conversion is done at the mid-market rate and the fee is very small. For even cheaper option, you can foresee a bit how much you will spend and "transform" some money on your card just once, thus your card effectively holding 2 currencies and using the best one for each payment. More details here: https://transferwise.com/gb/borderless/
So if you use a credit card card, the problem can be avoided altogether. And if it is multi-currency, it can be significantly cheaper than your standard bank.
* I am not affiliated in any way, I just like their product.
**Some shops, like the post office, do not accept credit cards, only maestro debit cards