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	$65.30	11.156%	$72.5849	$72.58	$72.60	$72.60
Purchase #2	$133.45	3.467%	$138.0767	$138.08	$138.10	$138.10
Purchase #3	$112.93	13.181%	$127.8153	$127.82	$127.80	$127.80
Purchase #4	$242.87	7.604%	$261.3378	$261.34	$261.35	$261.30
Purchase #5	$53.96	9.452%	$59.0603	$59.06	$59.05	$59.10
Purchase #6	$68.52	13.567%	$77.8161	$77.82	$77.80	$77.80
Purchase #7	$143.91	11.333%	$160.2193	$160.22	$160.20	$160.20
7 purchase totals =	$820.94		$896.9104	$896.92	$896.90	$896.90