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	$137.87	5.853%	$145.9395	$145.94	$145.95	$145.90
Purchase #2	$79.90	4.239%	$83.287	$83.29	$83.30	$83.30
Purchase #3	$52.99	6.551%	$56.4614	$56.46	$56.45	$56.50
Purchase #4	$190.38	10.186%	$209.7721	$209.77	$209.75	$209.80
Purchase #5	$131.30	7.780%	$141.5151	$141.52	$141.50	$141.50
Purchase #6	$205.40	12.117%	$230.2883	$230.29	$230.30	$230.30
Purchase #7	$31.58	13.531%	$35.8531	$35.85	$35.85	$35.90
7 purchase totals =	$829.42		$903.1165	$903.12	$903.10	$903.20