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	$139.73	10.583%	$154.5176	$154.52	$154.50	$154.50
Purchase #2	$202.84	12.865%	$228.9354	$228.94	$228.95	$228.90
Purchase #3	$146.78	8.212%	$158.8336	$158.83	$158.85	$158.80
Purchase #4	$81.64	8.104%	$88.2561	$88.26	$88.25	$88.30
Purchase #5	$81.31	10.133%	$89.5491	$89.55	$89.55	$89.50
Purchase #6	$62.85	6.295%	$66.8064	$66.81	$66.80	$66.80
Purchase #7	$249.41	11.708%	$278.6109	$278.61	$278.60	$278.60
7 purchase totals =	$964.56		$1,065.5091	$1,065.52	$1,065.50	$1,065.40