Leave the risk-free interest rate at 5% or below as it won't really factor into the equation that much. Enter the current price, the strike price, the length of the option (in days on the one I posted I believe), and then the volatility. I never actually calculate the real volatility, but rather just guess-timate it. Seeing how cryptos are highly prone to large run ups and huge sell-offs, I usually keep this in the 75-85% range.
You can read more about implied volatility here if you really wish to calculate it out:
http://www.utdallas.edu/~tday/6310FAQ3.html75-85% range should be good. The lower you go, the cheaper the option will be, but not by a whole lot. Remember, if you're selling covered call options then it technically means you think the "stock" (in this case LTC) will not exceed that price before expiration, or that you don't mind selling it for that price from now until expiration. If you're short term bearish, but long term bullish, you should sell short-dated call options (1-3 months max), and offer to buy long-dated put options from people. LTC could still swing violently on long-dated puts, though, so I suggest avoiding them honestly. People could get the calls and basically trade the swings a lot easier without having to day trade as much.
Example:
I buy a 2,500 LTC put option from you with a $3 strike that expires 6 months from now. This means I call sell you 2,500LTC @ $3 = $7500. I don't actually have to hold any LTC myself by doing this, only just pay the premium to get the guarantee.
Now, if LTC take a dive to $2/LTC, even for just a few hours, I could buy 2,500LTC @ $2 and sell to you for an extra $1/LTC. This only costs me $5k, but you give me $7.5k for them. As long as LTC is still trading low, I would then have an extra $2.5k (minus whatever the initial fee was) to buy "free" LTC and take out my $5k investment. If I think LTC will rebound, I buy the LTC and either sell when it recovers or ask for another put option from you (protecting my free money).
Keep your calls and/or puts short-dated. You could even offer "weekly" options if there were any interest in them. If you continue to offer these sorts of contracts, I strongly suggest that you sit down and read more about calls and puts to understand how to better make yourself more money and not just make everyone else rich. Cryptos aren't stocks and have shown to be much more violent when it comes to price swings. This creates what is called a high "beta", which in turn increases the value of the options being traded.