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	$122.55	13.829%	$139.4974	$139.50	$139.50	$139.50
Purchase #2	$227.61	4.671%	$238.2417	$238.24	$238.25	$238.20
Purchase #3	$149.27	6.160%	$158.465	$158.47	$158.45	$158.50
Purchase #4	$247.37	10.739%	$273.9351	$273.94	$273.95	$273.90
Purchase #5	$128.82	10.414%	$142.2353	$142.24	$142.25	$142.20
Purchase #6	$47.43	6.639%	$50.5789	$50.58	$50.60	$50.60
Purchase #7	$151.74	9.173%	$165.6591	$165.66	$165.65	$165.70
7 purchase totals =	$1,074.79		$1,168.6125	$1,168.63	$1,168.65	$1,168.60