As Russ says an indexer would do what you wanted but if using Mach it would likely be easy enough to do with a few buttons on a screen which you could make up.
Making a simple screen, with a Home button, maybe a DRO and a few buttons to move different increments would take you 5 mins to make.
The buttons would just contain some VB, for example
Code ("G91G0X10")
That would move in 10mm increments.
Code ("G91G0X1")
That would move 1mm increments
Code ("G91G0X-10")
Would move back 10mm increments etc etc, sure you get the idea.
Any help you needed you will get here on this forum, its full of great people.
Hood