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	$129.62	4.732%	$135.7536	$135.75	$135.75	$135.80
Purchase #2	$249.71	12.286%	$280.3894	$280.39	$280.40	$280.40
Purchase #3	$208.30	3.393%	$215.3676	$215.37	$215.35	$215.40
Purchase #4	$130.32	11.162%	$144.8663	$144.87	$144.85	$144.90
Purchase #5	$189.39	13.669%	$215.2777	$215.28	$215.30	$215.30
Purchase #6	$128.40	13.292%	$145.4669	$145.47	$145.45	$145.50
Purchase #7	$155.66	10.814%	$172.4931	$172.49	$172.50	$172.50
7 purchase totals =	$1,191.40		$1,309.6146	$1,309.62	$1,309.60	$1,309.80