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	$12.70	5.258%	$13.3678	$13.37	$13.35	$13.40
Purchase #2	$152.41	13.578%	$173.1042	$173.10	$173.10	$173.10
Purchase #3	$180.29	13.169%	$204.0324	$204.03	$204.05	$204.00
Purchase #4	$25.98	13.501%	$29.4876	$29.49	$29.50	$29.50
Purchase #5	$77.40	6.432%	$82.3784	$82.38	$82.40	$82.40
Purchase #6	$55.75	10.514%	$61.6116	$61.61	$61.60	$61.60
Purchase #7	$26.28	6.469%	$27.9801	$27.98	$28.00	$28.00
7 purchase totals =	$530.81		$591.9621	$591.96	$592.00	$592.00