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	$167.26	9.680%	$183.4508	$183.45	$183.45	$183.50
Purchase #2	$70.82	9.816%	$77.7717	$77.77	$77.75	$77.80
Purchase #3	$54.87	7.839%	$59.1713	$59.17	$59.15	$59.20
Purchase #4	$155.46	12.239%	$174.4867	$174.49	$174.50	$174.50
Purchase #5	$101.52	9.408%	$111.071	$111.07	$111.05	$111.10
Purchase #6	$29.60	13.333%	$33.5466	$33.55	$33.55	$33.50
Purchase #7	$138.56	8.734%	$150.6618	$150.66	$150.65	$150.70
7 purchase totals =	$718.09		$790.1599	$790.16	$790.10	$790.30