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	$17.73	11.757%	$19.8145	$19.81	$19.80	$19.80
Purchase #2	$165.86	4.591%	$173.4746	$173.47	$173.45	$173.50
Purchase #3	$55.66	3.132%	$57.4033	$57.40	$57.40	$57.40
Purchase #4	$10.75	4.196%	$11.2011	$11.20	$11.20	$11.20
Purchase #5	$98.94	12.670%	$111.4757	$111.48	$111.50	$111.50
Purchase #6	$137.26	4.790%	$143.8348	$143.83	$143.85	$143.80
Purchase #7	$83.99	6.353%	$89.3259	$89.33	$89.35	$89.30
7 purchase totals =	$570.19		$606.5299	$606.52	$606.55	$606.50