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	$129.55	12.587%	$145.8565	$145.86	$145.85	$145.90
Purchase #2	$158.80	6.255%	$168.7329	$168.73	$168.75	$168.70
Purchase #3	$210.95	8.615%	$229.1233	$229.12	$229.10	$229.10
Purchase #4	$92.51	8.504%	$100.3771	$100.38	$100.40	$100.40
Purchase #5	$153.46	7.197%	$164.5045	$164.50	$164.50	$164.50
Purchase #6	$10.51	3.352%	$10.8623	$10.86	$10.85	$10.90
Purchase #7	$59.39	4.714%	$62.1896	$62.19	$62.20	$62.20
7 purchase totals =	$815.17		$881.6462	$881.64	$881.65	$881.70