GST works the same way as all other taxes worked on the products. It simply omits the multiple number of taxes that demanded complex equations. Calculating tax on one product once and calculating multiple taxes on one product will fetch the same result but the second case is more time consuming.
GST is implemented in order to save time and sum up all the taxes that are applied at various levels of product manufacturing. The effect on change in prices is minimum on majority of products while certain products will get a considerable hike. First week of implementation will bring the actual results for sure.