As people have said in the comments you should as as much information as possible about your setup so that we can provide accurate results.
Exp:resso Store
If you are using Exp:resso Store there are a few options you can use. To display item specific sales tax you would want to use item_tax
tag inside of the items loop
{items}
Item Tax = {item_tax}
{/items}
If you want to display the tax for the entire order there are a couple tags you can use as mentioned in the docs
{order_subtotal_tax} = All the tax that is applicable to the orders subtotal
{order_shipping_tax} = The tax that is applicable to the shipping cost
{order_tax} = All the tax applicable to the entire order (includes subtotal and shipping)
You can also display the tax information such as name and rate with the followingL
{tax_name} = Value for the tax rate based upon your settings in the CP
{tax_rate} = Value like "0.10"
{tax_percentage} = Value like "10%"
CartThrob
If you are using CartThrob you would need to add the custom fields that you assigned to store tax, subtotal plus tax, shipping plus tax fields depending on what you want.
BrilliantRetail
If you are using BrilliantRetail you would want to use something like this I haven't used BR in a really long time so I am not 100% sure of their tag structure but looking through the included templates should help.