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	$158.51	13.874%	$180.5017	$180.50	$180.50	$180.50
Purchase #2	$100.36	12.314%	$112.7183	$112.72	$112.70	$112.70
Purchase #3	$17.88	13.684%	$20.3267	$20.33	$20.35	$20.30
Purchase #4	$38.92	10.198%	$42.8891	$42.89	$42.90	$42.90
Purchase #5	$92.71	13.247%	$104.9913	$104.99	$105.00	$105.00
Purchase #6	$178.60	3.158%	$184.2402	$184.24	$184.25	$184.20
Purchase #7	$188.33	13.634%	$214.0069	$214.01	$214.00	$214.00
7 purchase totals =	$775.31		$859.6742	$859.68	$859.70	$859.60