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	$70.76	12.521%	$79.6199	$79.62	$79.60	$79.60
Purchase #2	$72.49	13.649%	$82.3842	$82.38	$82.40	$82.40
Purchase #3	$65.58	10.594%	$72.5275	$72.53	$72.55	$72.50
Purchase #4	$50.68	4.863%	$53.1446	$53.14	$53.15	$53.10
Purchase #5	$169.86	7.111%	$181.9387	$181.94	$181.95	$181.90
Purchase #6	$80.39	9.623%	$88.1259	$88.13	$88.15	$88.10
Purchase #7	$11.38	11.241%	$12.6592	$12.66	$12.65	$12.70
7 purchase totals =	$521.14		$570.4000	$570.40	$570.45	$570.30