Hello @yang6,
So this fuction hist_boxplot
is very peculiar. I was hoping we can pass it to an assignment and then just round the values. It turned out not to work.
You'll see that I opened up the hist_boxplot
function, created my own and applied rounding on certain parts. You can essentially adjust the rounding in the plot function like I did and then run it. See the result below 
options(scipen=999)
data_set <- c(12.05, 10.22, 11.99, 13.22, 13.99, 12.55, 15.88, 16.88, 13.55, 16.77, 12.66)
library(survival)
library(packHV)
library(tidyverse)
custom_hist_boxplot <-
function (x, freq = TRUE, density = FALSE, main = NULL, xlab = NULL,
ymax = NULL, ...)
{
abs <- deparse(substitute(x))
if (is.null(xlab)) {
xlab = abs
}
ted <- hist(x, plot = FALSE)
par(yaxs = "i")
if (freq) {
ylim = c(-(max(ted$counts)/5), max(ted$counts)) %>% round(2)
boxwex = max(ted$counts)/6
}
else {
if (density) {
max = max(max(density(x)$y), max(ted$density)) %>% round(2)
}
else {
max = max(ted$density) %>% round(2)
}
ylim = c(-max/5, max) %>% round(2)
boxwex = max/6 %>% round(2)
}
if (!is.null(ymax))
ylim <- c(-ymax/5, ymax)
if (is.null(main)) {
main = paste("Histogram of", abs)
}
hist(x, ylim = ylim, yaxt = "n", xlab = xlab, freq = freq,
main = main, ...)
axis(2, at = seq(0, ylim[2], length = 5))
usrs <- par()$usr
par(new = TRUE, bty = "n", xaxs = "i", yaxs = "i",
ann = FALSE)
boxplot(x, horizontal = TRUE, ylim = usrs[1:2], add = TRUE,
at = usrs[3]/2, pars = list(boxwex = 5), col = "lightblue",
boxwex = ylim[2]/6)
if (density) {
lines(density(x), lwd = 2, col = "red")
}
}
custom_hist_boxplot(data_set, freq = FALSE, density = TRUE)

Created on 2020-10-10 by the reprex package (v0.3.0)