Some tokens, such as Safemoon, have buy/sell taxes built directly into their smart contracts. Reflection-based tokens use buy/sell taxes to create a trickle of tokens from each sell that can serve many purposes - small payouts to holders, auto-generating liquidity, and more.
If a token has a buy tax, you will notice that you receive fewer tokens than you otherwise would if there was no buy tax. When manually calculating total fees, it's wise to consider these built-in buy taxes in addition to DEX fees and our 1% convenience fee. This type of tax is up to the developers of a given protocol and we have no control over this.