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	$133.62	11.170%	$148.5454	$148.55	$148.55	$148.50
Purchase #2	$95.59	13.307%	$108.3102	$108.31	$108.30	$108.30
Purchase #3	$176.31	10.376%	$194.6039	$194.60	$194.60	$194.60
Purchase #4	$111.96	13.719%	$127.3198	$127.32	$127.30	$127.30
Purchase #5	$138.92	4.429%	$145.0728	$145.07	$145.05	$145.10
Purchase #6	$70.98	12.595%	$79.9199	$79.92	$79.90	$79.90
Purchase #7	$78.51	6.840%	$83.8801	$83.88	$83.90	$83.90
7 purchase totals =	$805.89		$887.6521	$887.65	$887.60	$887.60