Time Format

Please try

=TEXT(MROUND(A3,"0:30"),"h.mm")

I was going to suggest the same solution as Bo_ry has offered ... but you need to be aware that it is a text value; it is not numeric and you will not be able to do arithemetic with it.

You can create a custom format [hh].mm for that.

using a cell format mask ensures that it is still a true time value with which you can calculate if you want.
If you use text() it will convert into text meaning you will need additional actions to use it in a calculation.

so even though they present the time in the same way there is a difference in the solution. so if you need to sum or do other calculations you may want to use the custom cellformat over the text formula

edit: changed format from hh\.mm to [hh].mm because if you want to sum and go over 24hrs you need to [] to show duration and also remembered the slash is not need for time format, the point is enough to use