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	$147.93	12.566%	$166.5189	$166.52	$166.50	$166.50
Purchase #2	$129.32	10.380%	$142.7434	$142.74	$142.75	$142.70
Purchase #3	$172.76	3.371%	$178.5837	$178.58	$178.60	$178.60
Purchase #4	$230.50	10.530%	$254.7717	$254.77	$254.75	$254.80
Purchase #5	$84.83	6.709%	$90.5212	$90.52	$90.50	$90.50
Purchase #6	$116.28	5.294%	$122.4359	$122.44	$122.45	$122.40
Purchase #7	$165.51	13.159%	$187.2895	$187.29	$187.30	$187.30
7 purchase totals =	$1,047.13		$1,142.8643	$1,142.86	$1,142.85	$1,142.80