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	$138.86	11.177%	$154.3804	$154.38	$154.40	$154.40
Purchase #2	$149.93	6.500%	$159.6755	$159.68	$159.70	$159.70
Purchase #3	$92.60	7.737%	$99.7645	$99.76	$99.75	$99.80
Purchase #4	$228.59	8.495%	$248.0087	$248.01	$248.00	$248.00
Purchase #5	$250.97	5.403%	$264.5299	$264.53	$264.55	$264.50
Purchase #6	$77.41	10.475%	$85.5187	$85.52	$85.50	$85.50
Purchase #7	$49.83	9.307%	$54.4677	$54.47	$54.45	$54.50
7 purchase totals =	$988.19		$1,066.3454	$1,066.35	$1,066.35	$1,066.40