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	$21.48	4.386%	$22.4221	$22.42	$22.40	$22.40
Purchase #2	$178.62	3.641%	$185.1236	$185.12	$185.10	$185.10
Purchase #3	$100.90	11.269%	$112.2704	$112.27	$112.25	$112.30
Purchase #4	$46.38	4.576%	$48.5023	$48.50	$48.50	$48.50
Purchase #5	$249.90	10.730%	$276.7143	$276.71	$276.70	$276.70
Purchase #6	$177.94	5.154%	$187.111	$187.11	$187.10	$187.10
Purchase #7	$225.56	5.580%	$238.1462	$238.15	$238.15	$238.10
7 purchase totals =	$1,000.78		$1,070.2899	$1,070.28	$1,070.20	$1,070.20