If I am interested in keeping track of the amount I have saved through coupon discounts, how can i Post the transaction on a ledger. Can't see discount falling into any category: asset, expense, liability, equity, or revenue.
The discount reduces your expense, but is not a revenue.
So what you should likely do is book them as an expense, but on the opposite side of the ledger (assuming double-entry book-keeping).
Hence, if you would normally credit an expense account when buying something, you would debit an expense account for the amount of the coupon when you use a discount coupon.
That will allow you to track the discount coupons that you use separately, as you can give them an expense account of their own.