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	$108.40	13.739%	$123.2931	$123.29	$123.30	$123.30
Purchase #2	$135.52	7.706%	$145.9632	$145.96	$145.95	$146.00
Purchase #3	$49.32	7.591%	$53.0639	$53.06	$53.05	$53.10
Purchase #4	$40.99	3.756%	$42.5296	$42.53	$42.55	$42.50
Purchase #5	$81.76	7.426%	$87.8315	$87.83	$87.85	$87.80
Purchase #6	$81.27	9.747%	$89.1914	$89.19	$89.20	$89.20
Purchase #7	$247.60	8.821%	$269.4408	$269.44	$269.45	$269.40
7 purchase totals =	$744.86		$811.3135	$811.30	$811.35	$811.30