GCT, the General Consumption Tax, is paid to the government by all legal businesses selling over j$10,000,000 annually. To display the tax separate or include it in the price is up to the business, but needs to be paid nevertheless.
Businesses including it in the price have to back out the tax and pay it.
Many businesses don't hit the $10,000,000 threshold so are not required to collect or pay.
Small, family run type businesses have no reason for a service charge as it was designed to even out the wage discrepancy for larger businesses with large staffs, most of whom never receive a tip.