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	$226.72	12.764%	$255.6585	$255.66	$255.65	$255.70
Purchase #2	$41.91	10.306%	$46.2292	$46.23	$46.25	$46.20
Purchase #3	$73.40	12.282%	$82.415	$82.42	$82.40	$82.40
Purchase #4	$184.62	4.786%	$193.4559	$193.46	$193.45	$193.50
Purchase #5	$237.27	7.125%	$254.1755	$254.18	$254.20	$254.20
Purchase #6	$202.39	4.178%	$210.8459	$210.85	$210.85	$210.80
Purchase #7	$173.84	3.845%	$180.5241	$180.52	$180.50	$180.50
7 purchase totals =	$1,140.15		$1,223.3041	$1,223.32	$1,223.30	$1,223.30