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	$89.56	10.606%	$99.0587	$99.06	$99.05	$99.10
Purchase #2	$118.71	3.236%	$122.5515	$122.55	$122.55	$122.60
Purchase #3	$78.52	4.243%	$81.8516	$81.85	$81.85	$81.90
Purchase #4	$210.76	9.468%	$230.7148	$230.71	$230.70	$230.70
Purchase #5	$153.50	13.258%	$173.851	$173.85	$173.85	$173.90
Purchase #6	$62.99	11.710%	$70.3661	$70.37	$70.35	$70.40
Purchase #7	$210.87	5.314%	$222.0756	$222.08	$222.10	$222.10
7 purchase totals =	$924.91		$1,000.4693	$1,000.47	$1,000.45	$1,000.70