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	$79.81	11.873%	$89.2858	$89.29	$89.30	$89.30
Purchase #2	$228.96	12.869%	$258.4249	$258.42	$258.40	$258.40
Purchase #3	$140.90	7.268%	$151.1406	$151.14	$151.15	$151.10
Purchase #4	$237.41	7.451%	$255.0994	$255.10	$255.10	$255.10
Purchase #5	$218.37	10.585%	$241.4845	$241.48	$241.50	$241.50
Purchase #6	$60.63	8.495%	$65.7805	$65.78	$65.80	$65.80
Purchase #7	$219.74	11.679%	$245.4034	$245.40	$245.40	$245.40
7 purchase totals =	$1,185.82		$1,306.6191	$1,306.61	$1,306.65	$1,306.60