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	$127.35	8.548%	$138.2359	$138.24	$138.25	$138.20
Purchase #2	$119.43	11.721%	$133.4284	$133.43	$133.45	$133.40
Purchase #3	$170.88	11.479%	$190.4953	$190.50	$190.50	$190.50
Purchase #4	$11.30	6.758%	$12.0637	$12.06	$12.05	$12.10
Purchase #5	$54.30	9.208%	$59.2999	$59.30	$59.30	$59.30
Purchase #6	$97.76	7.633%	$105.222	$105.22	$105.20	$105.20
Purchase #7	$18.64	5.654%	$19.6939	$19.69	$19.70	$19.70
7 purchase totals =	$599.66		$658.4391	$658.44	$658.45	$658.40