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	$100.73	10.765%	$111.5736	$111.57	$111.55	$111.60
Purchase #2	$229.87	6.507%	$244.8276	$244.83	$244.85	$244.80
Purchase #3	$221.60	13.504%	$251.5249	$251.52	$251.50	$251.50
Purchase #4	$59.88	11.358%	$66.6812	$66.68	$66.70	$66.70
Purchase #5	$167.77	10.694%	$185.7113	$185.71	$185.70	$185.70
Purchase #6	$228.94	10.202%	$252.2965	$252.30	$252.30	$252.30
Purchase #7	$65.44	7.486%	$70.3388	$70.34	$70.35	$70.30
7 purchase totals =	$1,074.23		$1,182.9539	$1,182.95	$1,182.95	$1,182.90