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	$78.53	6.389%	$83.5473	$83.55	$83.55	$83.50
Purchase #2	$157.88	10.694%	$174.7637	$174.76	$174.75	$174.80
Purchase #3	$73.56	10.643%	$81.389	$81.39	$81.40	$81.40
Purchase #4	$187.64	3.117%	$193.4887	$193.49	$193.50	$193.50
Purchase #5	$145.55	10.325%	$160.578	$160.58	$160.60	$160.60
Purchase #6	$40.40	5.244%	$42.5186	$42.52	$42.50	$42.50
Purchase #7	$187.45	9.366%	$205.0066	$205.01	$205.00	$205.00
7 purchase totals =	$871.01		$941.2919	$941.30	$941.30	$941.30