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	$242.51	8.621%	$263.4168	$263.42	$263.40	$263.40
Purchase #2	$51.33	9.698%	$56.308	$56.31	$56.30	$56.30
Purchase #3	$63.91	9.823%	$70.1879	$70.19	$70.20	$70.20
Purchase #4	$15.99	13.123%	$18.0884	$18.09	$18.10	$18.10
Purchase #5	$118.38	8.288%	$128.1913	$128.19	$128.20	$128.20
Purchase #6	$99.31	5.870%	$105.1395	$105.14	$105.15	$105.10
Purchase #7	$75.58	10.410%	$83.4479	$83.45	$83.45	$83.40
7 purchase totals =	$667.01		$724.7798	$724.79	$724.80	$724.70