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	$64.38	12.436%	$72.3863	$72.39	$72.40	$72.40
Purchase #2	$26.91	8.335%	$29.1529	$29.15	$29.15	$29.20
Purchase #3	$159.27	11.822%	$178.0989	$178.10	$178.10	$178.10
Purchase #4	$68.49	5.807%	$72.4672	$72.47	$72.45	$72.50
Purchase #5	$163.46	4.612%	$170.9988	$171.00	$171.00	$171.00
Purchase #6	$79.83	13.582%	$90.6725	$90.67	$90.65	$90.70
Purchase #7	$205.32	5.393%	$216.3929	$216.39	$216.40	$216.40
7 purchase totals =	$767.66		$830.1695	$830.17	$830.15	$830.30