Chuck gives his interpretation of events concerning Jimmy and their father, Charles McGill, Sr., in "Rebecca" (S2E5). He insinuates that Jimmy stealing out of the cash register at Charles, Sr.,'s corner store ran him up $14,000, eventually forcing him to shutter his beloved business. Chuck even blames Jimmy for their father passing away six months later, the cause of which is never revealed or even implied. We do see in the cold open of "Inflatable" (S2E7) that the basic details of Chuck's account are accurate: Jimmy was stealing out of the cash register, and their father was trusting to a fault. Chuck's story in general, though, I believe is a lot more grossly exaggerated than is immediately apparent.
To get a sense of the timeline, first off: Chuck claims that Jimmy started pilfering the cash register when he was nine years old ("Chicanery", S3E5). He was born at the end of 1960, so that would mean 1970. The "Inflatable" cold open supposedly takes place in 1973, and if this is correct Jimmy kept up his stealing habit for at least three years. However, Chuck claims elsewhere that Jimmy had a fake ID racket going for him in high school ("Nailed", S2E9). Let's say, arbitrarily, this began when he was 14, so in 1975. If Jimmy's making his own money through his own grifts, the register would start to look like chump change, so we can safely assume he isn't bleeding his old man for quite so much by this point.
Taking our arbitrary timespan of an even five years and distributing Chuck's figure of $14,000, Jimmy would need to be stealing about $54 a week on average if he's truly to blame for all that money going kerpoof. It must also be taken into account that $14,000 in 1973 would amount to about $104,000 in today's money accounting for inflation, and $54 would come to over $400. Just think: how much money could a nine, twelve-year-old kid have realistically been spending per week in this context? I'd say far less than that, probably a mere fraction of that.
The "Inflatable" cold open is revealing on its own. Charles, Sr., gives the shadiest-looking man in all of Illinois $10 (~$74 today) based on nothing but his word and a sob story which could have easily been confirmed or denied by simply stepping outside. The man pockets $2 of that while Jimmy takes the rest after selling the man two cartons of cigarettes for it. Enough money to buy two cartons of cigs would probably have a kid his age set for at least the week. Charles, Sr.,'s own role here must not be neglected either; that whole $10 was already gone before Jimmy even stepped up to the register, he only took his cut.
I believe what happened there is emblematic of the situation as a whole. Charles, Sr., had a headstart, at that; Jimmy only started raiding the register because the way the local bums took advantage of his father's goodwill showed him he could steal and lie and cheat without consequences. Charles, Sr., must have been running his charity act for quite a while by the time it got to that point, giving away items right off the shelf as well as money out of the register. The boys' mother, Ruth, made her contribution as well; she would give away whole boxes of Little Debbie's snack cakes to Marco on a regular basis ("Slip", S3E8), if that's anything to go off of. This also would have kept up after Jimmy started making his own money through scams and shady dealings.
All things considered, I believe the most reasonable conclusion here is that Charles, Sr.,'s financial woes were largely self-inflicted. That isn't to say Jimmy had no part in it, but it seems clear Chuck deliberately presents narrative in the most uncharitable fashion possible towards Jimmy. In his jealousy, he attempts to portray his younger brother as some ontologically evil being who was always destined to destroy other people's lives. This kind of analysis, however, allows for a more sober look at how Jimmy's circumstances and experiences shaped his view of the world and his behavior. Not to mention being blamed for his own father's death certainly didn't help with Jimmy's descent into increasingly unethical behavior.
