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	$71.48	9.365%	$78.1741	$78.17	$78.15	$78.20
Purchase #2	$127.26	11.636%	$142.068	$142.07	$142.05	$142.10
Purchase #3	$193.47	11.258%	$215.2509	$215.25	$215.25	$215.30
Purchase #4	$145.87	6.613%	$155.5164	$155.52	$155.50	$155.50
Purchase #5	$39.47	11.554%	$44.0304	$44.03	$44.05	$44.00
Purchase #6	$225.62	13.776%	$256.7014	$256.70	$256.70	$256.70
Purchase #7	$15.69	12.268%	$17.6148	$17.61	$17.60	$17.60
7 purchase totals =	$818.86		$909.3560	$909.35	$909.30	$909.40