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	$168.38	8.861%	$183.3002	$183.30	$183.30	$183.30
Purchase #2	$224.81	12.323%	$252.5133	$252.51	$252.50	$252.50
Purchase #3	$213.87	7.660%	$230.2524	$230.25	$230.25	$230.30
Purchase #4	$92.31	8.241%	$99.9173	$99.92	$99.90	$99.90
Purchase #5	$31.26	6.460%	$33.2794	$33.28	$33.30	$33.30
Purchase #6	$38.58	10.140%	$42.492	$42.49	$42.50	$42.50
Purchase #7	$158.46	9.561%	$173.6104	$173.61	$173.60	$173.60
7 purchase totals =	$927.67		$1,015.3650	$1,015.36	$1,015.35	$1,015.40