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	$189.75	8.239%	$205.3835	$205.38	$205.40	$205.40
Purchase #2	$22.58	9.681%	$24.766	$24.77	$24.75	$24.80
Purchase #3	$132.45	7.144%	$141.9122	$141.91	$141.90	$141.90
Purchase #4	$29.83	10.814%	$33.0558	$33.06	$33.05	$33.10
Purchase #5	$20.67	13.337%	$23.4268	$23.43	$23.45	$23.40
Purchase #6	$100.59	10.563%	$111.2153	$111.22	$111.20	$111.20
Purchase #7	$114.74	12.314%	$128.8691	$128.87	$128.85	$128.90
7 purchase totals =	$610.61		$668.6287	$668.64	$668.60	$668.70