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	$65.49	8.791%	$71.2472	$71.25	$71.25	$71.20
Purchase #2	$115.55	10.161%	$127.291	$127.29	$127.30	$127.30
Purchase #3	$108.97	13.468%	$123.6461	$123.65	$123.65	$123.60
Purchase #4	$73.92	8.455%	$80.1699	$80.17	$80.15	$80.20
Purchase #5	$49.50	13.248%	$56.0578	$56.06	$56.05	$56.10
Purchase #6	$54.30	9.638%	$59.5334	$59.53	$59.55	$59.50
Purchase #7	$9.33	7.754%	$10.0534	$10.05	$10.05	$10.10
7 purchase totals =	$477.06		$527.9988	$528.00	$528.00	$528.00