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	$233.60	5.852%	$247.2703	$247.27	$247.25	$247.30
Purchase #2	$135.48	9.788%	$148.7408	$148.74	$148.75	$148.70
Purchase #3	$129.52	11.275%	$144.1234	$144.12	$144.10	$144.10
Purchase #4	$79.25	5.600%	$83.688	$83.69	$83.70	$83.70
Purchase #5	$106.89	4.233%	$111.4147	$111.41	$111.40	$111.40
Purchase #6	$185.71	6.400%	$197.5954	$197.60	$197.60	$197.60
Purchase #7	$58.70	9.718%	$64.4045	$64.40	$64.40	$64.40
7 purchase totals =	$929.15		$997.2371	$997.23	$997.20	$997.20