As it may be more convenient to obtain postage stamps of all one [or few] denomination[s] - even as coins are available in [few] denominations - I suggest we set the postage weights to compensate: where for example, first-class postage is $0.34 for the first ounce, and $0.31 per successive ounces, in effect successive $0.34 stamps would cover 34/31sts of a ounce, about 1.1 ounces.
Of course, if p-mail were ever efficient, the post-office would have long-ago converted prices to counting and weighing, and charging accordingly to the penny-precision ... and this article would have been moot a century ago - back then of course, the price of mailing first class, was, but a penny; and in the intervening decades the weight and strength of various papers has improved, so the five sheets of 8.5x11" 20# bond [four sheets of 24#] in a medium envelope, for one ounce total, could have been replaced by the half-ounce or quarter-ounce.
Someday maybe the post-office may offer domestic aerograms [weighing but a gram] - no envelope, just fold and seal - but by then we'd have gone all digitally secured e-mail.