Sales document number jumps by 10

Hi,

Sales document number range is jumping by 10 in production system.I checked number range object(T-code snum,object:crm_sales),but this will have all document types(all sales transactions). In my case only for one document type(ZXXX) the number range jump happens by 10.I checked snum transaction and buffering is 10.(the same setting is in Quality also,there the jump is not happening).Only for this particular document type I want to have a sequential number range.

Pls suggest.

Regards

Jaya