Craps - Buy Bets (in LV)

Alright so I've been fascinated with the buy bets on the outside numbers. Last trip I would buy 4/10 for $25 each and every MGM property asked for the vig only after a win... so $25 pays $49.

I hoping that someone could answer a couple of questions for me... specifically in Vegas (MGM properties) but anywhere that only charges the vig after is fine. First of all, does anyone allow you to go up to $30 with only a $1 vig (ie: 59 to 30). How does Harrah's treat buy bets? I'd highly doubt they charge the vig up front (that would be ridiculous with MGM next door, but so is the field) but I'm wondering how high they let you go.

Most strip locations and off strip locations throughout vegas allow you to pay the vig only after a win. Specifically: All Station Casinos (I have played Boulder, Santa Fe, Sunset, Palace and Texas), Most Boyd locations (I have played Samstown, Gold Coast, Orleans)

Typically they will charge you $1 up to $25, $2 from $30 to 50, $3 to $55 to 60, and $4 up to $80

I have questions about buy bets and I know it varies by place. But I think it might be easier to ask here for a "general" answer as opposed to walking up to dealers at different locations to ask each time I play. So if you take down a buy bet before the outcome of that bet is decided, does the vig get returned to you? Also, with the rounding up and down deal when it comes to vig calculations, do almost all places round up or down. What I mean is that let's say the vig is $1.25, do they usually round it down to a dollar? If the vig is $1.75, then they round the vig up to $2? Do they also try to "remember" previous bets? What I mean is let's say they rounded down the vig the last time from $1.25 to $1, and you make the same bet, would they ask you to pay $2 this time? If I am unclear, then please let me know. Thanks.