You could adjust the tolerance via the history. Also you could create a MEL script for each one from 0.1 to 1 using:

$selected = `ls -sl`;
for( $vert in $selected ) {
//Merge the Selected Vertices
polyMergeVertex -d 0.1 $vert;
};

$selected = `ls -sl`;
for( $vert in $selected ) {
//Merge the Selected Vertices
polyMergeVertex -d 0.2 $vert;
};

etc...

Hope this helps...