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	$151.50	3.253%	$156.4283	$156.43	$156.45	$156.40
Purchase #2	$158.87	10.870%	$176.1392	$176.14	$176.15	$176.10
Purchase #3	$114.50	11.603%	$127.7854	$127.79	$127.80	$127.80
Purchase #4	$20.53	4.700%	$21.4949	$21.49	$21.50	$21.50
Purchase #5	$158.48	12.766%	$178.7116	$178.71	$178.70	$178.70
Purchase #6	$197.58	7.436%	$212.272	$212.27	$212.25	$212.30
Purchase #7	$102.71	13.587%	$116.6652	$116.67	$116.65	$116.70
7 purchase totals =	$904.17		$989.4966	$989.50	$989.50	$989.50