Retirement Enhancement and Savings Act of 2018 This bill amends the Internal Revenue Code and the Employee Retirement Income Security Act of 1974 (ERISA) to modify requirements for tax-favored retirement savings accounts, employer-provided retirement plans, and retirement benefits for federal judges. With respect to employer-provided plans, the bill modifies requirements regarding: multiple employer plans, automatic enrollment and nonelective contributions, loans, terminating or transferring plans, reporting and disclosure rules, nondiscrimination rules, selecting lifetime income providers, and Pension Benefit Guaranty Corporation premiums. The bill also increases the tax credit for small employer pension plan startup costs and allows a tax credit for small employers that establish retirement plans that include automatic enrollment. With respect to Individual Retirement Accounts (IRAs), the bill: treats taxable non-tuition fellowship and stipend payments as compensation, repeals the maximum age for traditional IRA contributions, and permits any IRA to be a shareholder of any S corporation that is a bank. The bill makes several modifications to retirement benefits for magistrate judges of the U.S. Tax Court and other federal judges. The bill also modifies various tax provisions to: reinstate and increase the tax exclusion for benefits provided to volunteer firefighters and emergency medical responders, revise the required distribution rules for pension plans, increase penalties for failing to file tax or retirement plan returns, and require the Internal Revenue Service to share returns and return information with U.S. Customs Border Protection to administer the heavy vehicle use tax.