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	$111.94	13.866%	$127.4616	$127.46	$127.45	$127.50
Purchase #2	$42.87	7.505%	$46.0874	$46.09	$46.10	$46.10
Purchase #3	$69.90	13.618%	$79.419	$79.42	$79.40	$79.40
Purchase #4	$67.98	5.771%	$71.9031	$71.90	$71.90	$71.90
Purchase #5	$151.82	9.447%	$166.1624	$166.16	$166.15	$166.20
Purchase #6	$229.71	12.260%	$257.8724	$257.87	$257.85	$257.90
Purchase #7	$91.35	10.757%	$101.1765	$101.18	$101.20	$101.20
7 purchase totals =	$765.57		$850.0824	$850.08	$850.05	$850.20