Practically speaking, there is no difference between "east" and "5 degrees south of east." You probably have a variation of 20 degrees just depending on where your siddur is on the table, or the way you "shukkel." One prominent posek said (half-jokingly) about this topic: לא ניתנה תורה למהנדסים - The Torah was not given to engineers. Therefore, you're probably safe if you aim for the nearest half-quadrant (e.g., N, NE, E, SE, etc.). With regard to a house that does not have a wall facing Jerusalem, it would depend how much of a discrepancy there is. It would only make sense to face a corner if there is a difference of more than 20 degrees or so, as mentioned above. This seems to be the "common custom" in shuls worldwide.
Two more points:
(1) There are differences of opinion as to whether one should face towards the direction that would be indicated by a standard Mercator Projection map, or rather following a Great Circle route, which is really a "straight line" towards Jerusalem. The difference in NY is more than 40 degrees! See here and here for good summaries of this topic. (2) A compass is not a precise way of determining direction, since the Earth's magnetic field is not completely parallel to its axis. There is an offset that depends on one's location, and that varies over time due to activity in the earth's core. It is therefore better to use a map with a "true north" indicator.