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	$131.49	12.705%	$148.1958	$148.20	$148.20	$148.20
Purchase #2	$47.70	6.321%	$50.7151	$50.72	$50.70	$50.70
Purchase #3	$155.25	12.461%	$174.5957	$174.60	$174.60	$174.60
Purchase #4	$114.60	11.429%	$127.6976	$127.70	$127.70	$127.70
Purchase #5	$46.88	5.653%	$49.5301	$49.53	$49.55	$49.50
Purchase #6	$212.30	6.519%	$226.1398	$226.14	$226.15	$226.10
Purchase #7	$172.33	7.554%	$185.3478	$185.35	$185.35	$185.30
7 purchase totals =	$880.55		$962.2219	$962.24	$962.25	$962.10