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	$135.52	6.704%	$144.6053	$144.61	$144.60	$144.60
Purchase #2	$11.85	6.294%	$12.5958	$12.60	$12.60	$12.60
Purchase #3	$107.55	9.741%	$118.0264	$118.03	$118.05	$118.00
Purchase #4	$100.60	7.371%	$108.0152	$108.02	$108.00	$108.00
Purchase #5	$49.34	9.627%	$54.09	$54.09	$54.10	$54.10
Purchase #6	$89.63	10.603%	$99.1335	$99.13	$99.15	$99.10
Purchase #7	$233.69	8.838%	$254.3435	$254.34	$254.35	$254.30
7 purchase totals =	$728.18		$790.8097	$790.82	$790.85	$790.70