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	$47.45	5.687%	$50.1485	$50.15	$50.15	$50.10
Purchase #2	$166.80	3.375%	$172.4295	$172.43	$172.45	$172.40
Purchase #3	$205.49	7.705%	$221.323	$221.32	$221.30	$221.30
Purchase #4	$170.68	10.821%	$189.1493	$189.15	$189.15	$189.10
Purchase #5	$129.49	11.128%	$143.8996	$143.90	$143.90	$143.90
Purchase #6	$47.73	6.839%	$50.9943	$50.99	$51.00	$51.00
Purchase #7	$244.76	4.456%	$255.6665	$255.67	$255.65	$255.70
7 purchase totals =	$1,012.40		$1,083.6107	$1,083.61	$1,083.60	$1,083.50