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	$29.85	4.380%	$31.1574	$31.16	$31.15	$31.20
Purchase #2	$222.94	8.437%	$241.7494	$241.75	$241.75	$241.70
Purchase #3	$61.82	6.737%	$65.9848	$65.98	$66.00	$66.00
Purchase #4	$105.30	3.155%	$108.6222	$108.62	$108.60	$108.60
Purchase #5	$122.43	4.201%	$127.5733	$127.57	$127.55	$127.60
Purchase #6	$167.25	4.334%	$174.4986	$174.50	$174.50	$174.50
Purchase #7	$149.53	5.844%	$158.2685	$158.27	$158.25	$158.30
7 purchase totals =	$859.12		$907.8542	$907.85	$907.80	$907.90