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	$11.90	6.283%	$12.6477	$12.65	$12.65	$12.60
Purchase #2	$75.79	4.208%	$78.9792	$78.98	$79.00	$79.00
Purchase #3	$148.32	5.445%	$156.396	$156.40	$156.40	$156.40
Purchase #4	$241.71	13.512%	$274.3699	$274.37	$274.35	$274.40
Purchase #5	$89.45	10.867%	$99.1705	$99.17	$99.15	$99.20
Purchase #6	$70.74	9.415%	$77.4002	$77.40	$77.40	$77.40
Purchase #7	$168.25	6.139%	$178.5789	$178.58	$178.60	$178.60
7 purchase totals =	$806.16		$877.5424	$877.55	$877.55	$877.60