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	$204.33	6.118%	$216.8309	$216.83	$216.85	$216.80
Purchase #2	$139.45	13.862%	$158.7806	$158.78	$158.80	$158.80
Purchase #3	$185.66	10.682%	$205.4922	$205.49	$205.50	$205.50
Purchase #4	$172.77	13.591%	$196.2512	$196.25	$196.25	$196.30
Purchase #5	$167.58	3.785%	$173.9229	$173.92	$173.90	$173.90
Purchase #6	$89.94	9.573%	$98.55	$98.55	$98.55	$98.60
Purchase #7	$180.83	5.254%	$190.3308	$190.33	$190.35	$190.30
7 purchase totals =	$1,140.56		$1,240.1586	$1,240.15	$1,240.20	$1,240.20