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	$179.74	4.487%	$187.8049	$187.80	$187.80	$187.80
Purchase #2	$105.73	4.466%	$110.4519	$110.45	$110.45	$110.50
Purchase #3	$13.67	11.738%	$15.2746	$15.27	$15.25	$15.30
Purchase #4	$172.50	10.767%	$191.0731	$191.07	$191.05	$191.10
Purchase #5	$97.54	5.870%	$103.2656	$103.27	$103.25	$103.30
Purchase #6	$118.54	5.565%	$125.1368	$125.14	$125.15	$125.10
Purchase #7	$118.68	7.672%	$127.7851	$127.79	$127.80	$127.80
7 purchase totals =	$806.40		$860.7920	$860.79	$860.75	$860.90