If you work from trade prices to create your Once catalogue, the Price Adjuster tool can be used to easily apply price increases (or decreases) to your original trade prices, meaning that you don't need to change your markup/discount.

If your supplier increases their prices by a certain percentage, you can quickly and easily apply this change to multiple products.

Open up the Price Calculator tool in Once Setup by pressing this button: 

Next, go to the Base prices % change tab

Check the boxes next to the products that you want to apply and increase to, and enter the percentage price change you wish to apply.  In the screenshot above, I want to apply a 2% increase to the base prices of my Metal Venetians and Perfect Fit products.

Click Apply. You will be asked if you want to make a backup of your prices, which is a good idea in case you have made any mistakes as you can easily get your old prices back.  After this, click Yes to change your prices.

You will see that your base prices have increased, and your existing markup/discounts are applied to the new base prices.  If you want to look at what your base prices are, you can check the Show base prices box on the prices tab of any product.