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	$249.59	8.379%	$270.5031	$270.50	$270.50	$270.50
Purchase #2	$145.86	3.461%	$150.9082	$150.91	$150.90	$150.90
Purchase #3	$234.39	9.712%	$257.154	$257.15	$257.15	$257.20
Purchase #4	$111.97	3.829%	$116.2573	$116.26	$116.25	$116.30
Purchase #5	$119.40	6.850%	$127.5789	$127.58	$127.60	$127.60
Purchase #6	$167.58	3.525%	$173.4872	$173.49	$173.50	$173.50
Purchase #7	$157.92	11.197%	$175.6023	$175.60	$175.60	$175.60
7 purchase totals =	$1,186.71		$1,271.4910	$1,271.49	$1,271.50	$1,271.60