I've seen some really out of level 10 gallon tanks in other people's fishrooms. Racks of them on end, partially supported, on bowing racks. Never heard of any problems, which is rather unbelievable. Just to see I left my 10 gallon stand, which holds 3 tanks stacked vertically, out of level by a good 1/4". It's been that way for a few months, and hasn't been any problem. I'll eventually level it, it's an easy enough job, and if a tank starts to leak 10 gallons are about as cheap as they come.
If you do want to level it, level the dresser with wedges, not the tank itself. I use wooden wedges designed for door & window installation.