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	$159.82	10.408%	$176.4541	$176.45	$176.45	$176.50
Purchase #2	$133.40	5.476%	$140.705	$140.71	$140.70	$140.70
Purchase #3	$44.68	4.443%	$46.6651	$46.67	$46.65	$46.70
Purchase #4	$226.89	6.864%	$242.4637	$242.46	$242.45	$242.50
Purchase #5	$44.80	4.492%	$46.8124	$46.81	$46.80	$46.80
Purchase #6	$52.32	5.593%	$55.2463	$55.25	$55.25	$55.20
Purchase #7	$70.27	3.651%	$72.8356	$72.84	$72.85	$72.80
7 purchase totals =	$732.18		$781.1822	$781.19	$781.15	$781.20