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	$183.84	3.636%	$190.5244	$190.52	$190.50	$190.50
Purchase #2	$74.43	10.376%	$82.1529	$82.15	$82.15	$82.20
Purchase #3	$232.90	4.451%	$243.2664	$243.27	$243.25	$243.30
Purchase #4	$21.65	6.505%	$23.0583	$23.06	$23.05	$23.10
Purchase #5	$65.45	3.212%	$67.5523	$67.55	$67.55	$67.60
Purchase #6	$44.66	10.870%	$49.5145	$49.51	$49.50	$49.50
Purchase #7	$109.35	8.460%	$118.601	$118.60	$118.60	$118.60
7 purchase totals =	$732.28		$774.6698	$774.66	$774.60	$774.80