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	$158.29	12.712%	$178.4118	$178.41	$178.40	$178.40
Purchase #2	$168.62	10.662%	$186.5983	$186.60	$186.60	$186.60
Purchase #3	$94.45	12.588%	$106.3394	$106.34	$106.35	$106.30
Purchase #4	$153.93	12.259%	$172.8003	$172.80	$172.80	$172.80
Purchase #5	$9.95	5.712%	$10.5183	$10.52	$10.50	$10.50
Purchase #6	$49.91	9.848%	$54.8251	$54.83	$54.85	$54.80
Purchase #7	$20.40	5.311%	$21.4834	$21.48	$21.50	$21.50
7 purchase totals =	$655.55		$730.9766	$730.98	$731.00	$730.90