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	$155.82	8.171%	$168.5521	$168.55	$168.55	$168.60
Purchase #2	$97.82	6.205%	$103.8897	$103.89	$103.90	$103.90
Purchase #3	$135.35	6.522%	$144.1775	$144.18	$144.20	$144.20
Purchase #4	$68.75	13.745%	$78.1997	$78.20	$78.20	$78.20
Purchase #5	$141.72	4.565%	$148.1895	$148.19	$148.20	$148.20
Purchase #6	$45.68	4.499%	$47.7351	$47.74	$47.75	$47.70
Purchase #7	$17.28	11.675%	$19.2974	$19.30	$19.30	$19.30
7 purchase totals =	$662.42		$710.0410	$710.05	$710.10	$710.10