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	$142.35	4.265%	$148.4212	$148.42	$148.40	$148.40
Purchase #2	$60.57	9.196%	$66.14	$66.14	$66.15	$66.10
Purchase #3	$50.55	6.548%	$53.86	$53.86	$53.85	$53.90
Purchase #4	$44.63	12.505%	$50.211	$50.21	$50.20	$50.20
Purchase #5	$143.61	13.395%	$162.8466	$162.85	$162.85	$162.80
Purchase #6	$181.77	13.128%	$205.6328	$205.63	$205.65	$205.60
Purchase #7	$166.83	8.865%	$181.6195	$181.62	$181.60	$181.60
7 purchase totals =	$790.31		$868.7311	$868.73	$868.70	$868.60