Rounding of a number to nearest tenth or hundredth means we approximate it and for this we do not need a number beyod tenth or hundredth,

As we have in decimal number system, a number from #0# to #9# at a place,

if we have a number from #0# to #4#, we remove the numbers beyond those desired completely - for example if a number is #3.14159# and we need to round it to nearest hundredth, as we have #1# next to number in hundredth place, we just ignore it and write #3.14#.

if we have a number from #5# to #9#, we remove the numbers completely, but add #1# to the last desired digit- for example in the given case #$21.38# and we need to round it to nearest tenth, as we have #8# next to number in tenth place, we ignore it but add #1# to #3#, which is the last digit and rounding #$21.38# to tenth place, it becomes #$21.40#.