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	$26.67	10.465%	$29.461	$29.46	$29.45	$29.50
Purchase #2	$138.58	4.675%	$145.0586	$145.06	$145.05	$145.10
Purchase #3	$129.31	8.346%	$140.1022	$140.10	$140.10	$140.10
Purchase #4	$15.32	13.465%	$17.3828	$17.38	$17.40	$17.40
Purchase #5	$53.37	4.820%	$55.9424	$55.94	$55.95	$55.90
Purchase #6	$90.87	13.774%	$103.3864	$103.39	$103.40	$103.40
Purchase #7	$71.31	11.533%	$79.5342	$79.53	$79.55	$79.50
7 purchase totals =	$525.43		$570.8676	$570.86	$570.90	$570.90