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	$77.76	4.812%	$81.5018	$81.50	$81.50	$81.50
Purchase #2	$43.73	6.425%	$46.5397	$46.54	$46.55	$46.50
Purchase #3	$217.71	12.406%	$244.7191	$244.72	$244.70	$244.70
Purchase #4	$103.36	13.462%	$117.2743	$117.27	$117.25	$117.30
Purchase #5	$103.75	7.247%	$111.2688	$111.27	$111.25	$111.30
Purchase #6	$51.80	9.461%	$56.7008	$56.70	$56.70	$56.70
Purchase #7	$100.87	7.471%	$108.406	$108.41	$108.40	$108.40
7 purchase totals =	$698.98		$766.4105	$766.41	$766.35	$766.40