A few comments:
It would be helpful to readers if you provided a 3-5 line overview of What the database is about, Without readers are guessing.
All tables should have a Primary Key defined - it should uniquely identify every record iin the table.
CustomerT does NOT have a PK
CustomerT should be related to OrderT 1 to Many (a customer can have many Orders)
What is the purpose of 2 copies of ProductT??
I doubt that Taxable/nonTaxable goes with Order ---probably Product.
You do NOT need Totals or SubTotals in Tables --calculate then in queries or reports when needed.
OrderDetailsT should record the Quantity(number of units) and Selling Price(per unit) of the Product. [If you don't do this you'll have trouble changing prices]
I would Not use multivalue or attachment fields in any Table ----Personal choice.
Seems you forgot CustomerId PK in CustomerT since you allowed for the FK in OrderT.
Always get your tables designed to meet your requirements before jumping in to Forms and Reports ---Personal Choice and highly recommended.
Good luck with your project.
See
this link for tutorial on database design/entity Diagramming.