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	$52.52	13.265%	$59.4868	$59.49	$59.50	$59.50
Purchase #2	$221.32	3.229%	$228.4664	$228.47	$228.45	$228.50
Purchase #3	$15.64	12.540%	$17.6013	$17.60	$17.60	$17.60
Purchase #4	$144.55	11.154%	$160.6731	$160.67	$160.65	$160.70
Purchase #5	$154.95	6.632%	$165.2263	$165.23	$165.25	$165.20
Purchase #6	$48.28	3.863%	$50.1451	$50.15	$50.15	$50.10
Purchase #7	$47.79	4.767%	$50.0681	$50.07	$50.05	$50.10
7 purchase totals =	$685.05		$731.6671	$731.68	$731.65	$731.70