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	$107.83	10.759%	$119.4314	$119.43	$119.45	$119.40
Purchase #2	$85.59	7.302%	$91.8398	$91.84	$91.85	$91.80
Purchase #3	$151.56	9.183%	$165.4778	$165.48	$165.50	$165.50
Purchase #4	$20.95	12.723%	$23.6155	$23.62	$23.60	$23.60
Purchase #5	$89.25	6.824%	$95.3404	$95.34	$95.35	$95.30
Purchase #6	$45.87	13.664%	$52.1377	$52.14	$52.15	$52.10
Purchase #7	$32.85	3.668%	$34.0549	$34.05	$34.05	$34.10
7 purchase totals =	$533.90		$581.8975	$581.90	$581.95	$581.80