Hello! You have two options:
1) Create a custom field where users can select how many tickets they want, then have the field calculate the price accordingly. Easy
Our custom selection fields video tutorial would be a big help to you on setting this up. One downside... while the price would be calculated, the record will still just count as ONE record towards your event capacity. That may or may not be an issue for you.
2) Use group registration
Now, be aware that next week we will be releasing a MASSIVE new version of DT Register that brings tons of great improvements to the table. In this new version, you'll have the option of "Simple Group Registration" so you can enter the number of members/tickets then go straight to the billing contact page... no entering data for each member.
If you don't need to launch right away, I'd suggest waiting for the new release then go with that. Otherwise, you'll probably need to use custom fields, which is what many people do. Thanks.