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	$55.93	3.847%	$58.0816	$58.08	$58.10	$58.10
Purchase #2	$95.94	4.375%	$100.1374	$100.14	$100.15	$100.10
Purchase #3	$219.34	8.767%	$238.5695	$238.57	$238.55	$238.60
Purchase #4	$107.55	10.252%	$118.576	$118.58	$118.60	$118.60
Purchase #5	$46.69	11.274%	$51.9538	$51.95	$51.95	$52.00
Purchase #6	$163.90	4.168%	$170.7314	$170.73	$170.75	$170.70
Purchase #7	$99.80	11.377%	$111.1542	$111.15	$111.15	$111.20
7 purchase totals =	$789.15		$849.2039	$849.20	$849.25	$849.30