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	$143.31	6.325%	$152.3744	$152.37	$152.35	$152.40
Purchase #2	$136.83	5.669%	$144.5869	$144.59	$144.60	$144.60
Purchase #3	$229.83	3.599%	$238.1016	$238.10	$238.10	$238.10
Purchase #4	$80.85	8.694%	$87.8791	$87.88	$87.90	$87.90
Purchase #5	$122.95	7.185%	$131.784	$131.78	$131.80	$131.80
Purchase #6	$64.28	13.564%	$72.9989	$73.00	$73.00	$73.00
Purchase #7	$235.45	6.856%	$251.5925	$251.59	$251.60	$251.60
7 purchase totals =	$1,013.50		$1,079.3174	$1,079.31	$1,079.35	$1,079.40