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	$100.43	11.254%	$111.7324	$111.73	$111.75	$111.70
Purchase #2	$230.94	11.404%	$257.2764	$257.28	$257.30	$257.30
Purchase #3	$94.82	10.169%	$104.4622	$104.46	$104.45	$104.50
Purchase #4	$86.60	3.420%	$89.5617	$89.56	$89.55	$89.60
Purchase #5	$209.39	10.104%	$230.5468	$230.55	$230.55	$230.50
Purchase #6	$143.60	5.729%	$151.8268	$151.83	$151.85	$151.80
Purchase #7	$33.93	7.860%	$36.5969	$36.60	$36.60	$36.60
7 purchase totals =	$899.71		$982.0032	$982.01	$982.05	$982.00