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	$7.66	12.366%	$8.6072	$8.61	$8.60	$8.60
Purchase #2	$186.38	4.555%	$194.8696	$194.87	$194.85	$194.90
Purchase #3	$77.52	10.296%	$85.5015	$85.50	$85.50	$85.50
Purchase #4	$21.57	4.848%	$22.6157	$22.62	$22.60	$22.60
Purchase #5	$62.38	13.198%	$70.6129	$70.61	$70.60	$70.60
Purchase #6	$163.82	8.704%	$178.0789	$178.08	$178.10	$178.10
Purchase #7	$83.52	7.693%	$89.9452	$89.95	$89.95	$89.90
7 purchase totals =	$602.85		$650.2310	$650.24	$650.20	$650.20