Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.94	7.257%	$97.5395	$97.54	$97.55	$97.50
Purchase #2	$63.52	9.466%	$69.5328	$69.53	$69.55	$69.50
Purchase #3	$10.40	3.795%	$10.7947	$10.79	$10.80	$10.80
Purchase #4	$224.33	4.565%	$234.5707	$234.57	$234.55	$234.60
Purchase #5	$19.80	10.488%	$21.8766	$21.88	$21.90	$21.90
Purchase #6	$75.82	8.592%	$82.3345	$82.33	$82.35	$82.30
Purchase #7	$73.62	11.302%	$81.9405	$81.94	$81.95	$81.90
7 purchase totals =	$558.43		$598.5893	$598.58	$598.65	$598.50