Create axis tick points

# enter a maximum value in your data and generate tick-points for a plot axis

yax <- function(x, tickabove = F, ntick = 5) {
  l <- c(c(1, 2, 4, 5, 25) %o% 10^(0:8))
  d <- l[which.min(abs(x/ntick - l))]
  d <- 0:(ntick+1) * d
  i <- findInterval(x, d)
  if (tickabove) {i <- i + 1}
  d[seq_len(i)]
}

# example

x <- lapply(rep(100, 4), rnorm, mean = 5, sd = 1.5)
y <- lapply(rep(100, 4), rnorm, mean = 4, sd = 1)
y <- mapply(`^`, x = y, y = 1:4, SIMPLIFY = F)

yaxes <- lapply(y, function(x) yax(max(x)))

par(mfrow = c(2, 2))
for(i in 1:4) {
  plot(x[[i]], y[[i]], axes = F, xlab = 'x', ylab = 'y', ylim = c(0, max(y[[i]])))
  axis(1)
  axis(2, yaxes[[i]], las = 2)
}