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	$16.60	3.349%	$17.1559	$17.16	$17.15	$17.20
Purchase #2	$59.30	6.313%	$63.0436	$63.04	$63.05	$63.00
Purchase #3	$15.77	10.772%	$17.4687	$17.47	$17.45	$17.50
Purchase #4	$43.99	4.140%	$45.8112	$45.81	$45.80	$45.80
Purchase #5	$222.55	12.391%	$250.1262	$250.13	$250.15	$250.10
Purchase #6	$66.34	7.774%	$71.4973	$71.50	$71.50	$71.50
Purchase #7	$115.27	10.542%	$127.4218	$127.42	$127.40	$127.40
7 purchase totals =	$539.82		$592.5247	$592.53	$592.50	$592.50