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	$166.27	4.213%	$173.275	$173.28	$173.30	$173.30
Purchase #2	$118.94	10.763%	$131.7415	$131.74	$131.75	$131.70
Purchase #3	$236.71	9.753%	$259.7963	$259.80	$259.80	$259.80
Purchase #4	$66.81	11.530%	$74.5132	$74.51	$74.50	$74.50
Purchase #5	$81.96	9.401%	$89.6651	$89.67	$89.65	$89.70
Purchase #6	$144.42	9.624%	$158.319	$158.32	$158.30	$158.30
Purchase #7	$19.78	8.466%	$21.4546	$21.45	$21.45	$21.50
7 purchase totals =	$834.89		$908.7647	$908.77	$908.75	$908.80