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	$27.82	9.517%	$30.4676	$30.47	$30.45	$30.50
Purchase #2	$95.76	13.742%	$108.9193	$108.92	$108.90	$108.90
Purchase #3	$25.51	5.425%	$26.8939	$26.89	$26.90	$26.90
Purchase #4	$233.27	12.730%	$262.9653	$262.97	$262.95	$263.00
Purchase #5	$123.89	6.395%	$131.8128	$131.81	$131.80	$131.80
Purchase #6	$79.76	13.326%	$90.3888	$90.39	$90.40	$90.40
Purchase #7	$111.95	13.574%	$127.1461	$127.15	$127.15	$127.10
7 purchase totals =	$697.96		$778.5938	$778.60	$778.55	$778.60