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	$240.86	10.633%	$266.4706	$266.47	$266.45	$266.50
Purchase #2	$185.50	9.207%	$202.579	$202.58	$202.60	$202.60
Purchase #3	$206.89	8.344%	$224.1529	$224.15	$224.15	$224.20
Purchase #4	$65.51	11.677%	$73.1596	$73.16	$73.15	$73.20
Purchase #5	$51.39	3.165%	$53.0165	$53.02	$53.00	$53.00
Purchase #6	$51.89	4.795%	$54.3781	$54.38	$54.40	$54.40
Purchase #7	$57.43	3.584%	$59.4883	$59.49	$59.50	$59.50
7 purchase totals =	$859.47		$933.2450	$933.25	$933.25	$933.40