a new hope - Why did the Imperial Star Destroyer open fire on the Tantive IV?

The opening shot of A New Hope features a fight in space between the rebel ship, the Tantive IV, and an Imperial Star Destroyer. I understand why the Tantive IV would be (uselessly) firing at the Empire's ship since the Rebels were running for their lives. But why would the Star Destroyer shoot at the Tantive IV? A misplaced shot could destroy the ship altogether. Indeed, at one point they hit the middle of the ship, causing an explosion.

It's my understanding that the Empire was trying to recover the stolen Death Star plans, not destroy them. They wanted to recapture the plans, detain the crew and probably torture them for information on the Rebellion. This is reflected in Vader's commands.

VADER: Commander, tear this ship apart until you've found those plans and bring me the passengers. I want them alive!

Since they were going to capture the Tantive IV in their tractor beam anyway why risk destroying the ship and its precious cargo?

Answer

The goal was to disable the ship with precision fire rather than destroying it. Their main targets were the ship's navigational array, solar fin and the engines at the rear of the ship. Hitting these left the ship with no navigation (and no hyperspace), no capacity to land and no sublight engines, making the Tantive IV easy prey.

Both vessels had just entered Tatooine’s orbit when the Devastator’s lasers scored a direct hit on the Tantive IV’s primary sensor array. The array exploded, and the blast overloaded the starboard shield projector — which caused another explosion, damaging the power generator system and triggering a chain reaction throughout the ship. With no starboard shield and no power to its engines, the Tantive IV was effectively crippled.

_{^{Star Wars: A New Hope - Junior Novelisation}}

and

One of those probing, questing beams succeeded in touching the fleeing ship, striking its principal solar fin. Gemlike fragments of metal and plastic erupted into space as the end of the fin disintegrated. The vessel seemed to shudder. ... “Yes, I suppose they did have to shut the drive down,” Threepio admitted, “but what are we going to do now? We can’t enter atmosphere with our main stabilizer fin destroyed. I can’t believe we’re simply going to surrender.”

_{^{Star Wars: A New Hope - Official Novelisation}}

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When they shut down the reactor (and with it the ship's guns) the Devastator immediately stopped firing and they tractored the ship into their main bay and prepared to board it.

Did you hear that?” C-3PO said to R2-D2 as the Tantive IV’s engines powered down. “They’ve shut down the main reactor. We’ll be destroyed for sure. This is madness!”

_{^{Star Wars: A New Hope - Junior Novelisation}}