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	$18.79	7.135%	$20.1307	$20.13	$20.15	$20.10
Purchase #2	$98.99	5.533%	$104.4671	$104.47	$104.45	$104.50
Purchase #3	$95.50	10.597%	$105.6201	$105.62	$105.60	$105.60
Purchase #4	$165.73	5.697%	$175.1716	$175.17	$175.15	$175.20
Purchase #5	$9.69	8.630%	$10.5262	$10.53	$10.55	$10.50
Purchase #6	$48.89	4.495%	$51.0876	$51.09	$51.10	$51.10
Purchase #7	$147.53	7.185%	$158.13	$158.13	$158.15	$158.10
7 purchase totals =	$585.12		$625.1333	$625.14	$625.15	$625.10