SliQ Invoicing is configurable as to whether it shows the net or gross value of a line item in the total column for an invoice or quote. By default SliQ shows the net total but you can change the option to show the gross value.
If you are using a standard template and have not edited the template to create a custom one, you can follow the advice in this help article:
However, if you are using SliQ Invoicing Plus and you have edited your template, you need to open up the template in the editor, click on the table of invoice items and choose the option to show the gross total in the properties panel on the right.
Here is a link to help on editing an invoice template: