You can change the Default sales tax rate for the Website, POS and Wedding/Event Proposals in Settings > Tax Rate. Using the radio button under the column for POS, Website and Proposal Manager, you can choose which tax rate is respectively applied to each form of sales.
Tax by Line
You can also turn on the Tax by Line feature which will allow you to choose which items on the proposal should receive tax.
- Enable this setting under Settings > Proposal Settings
- Set "Tax by line" to Yes
- On the proposal, use the checkbox next to the product to select which items do not get taxed (if checked, tax will be applied)