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	$138.51	4.339%	$144.5199	$144.52	$144.50	$144.50
Purchase #2	$169.62	4.123%	$176.6134	$176.61	$176.60	$176.60
Purchase #3	$85.61	12.561%	$96.3635	$96.36	$96.35	$96.40
Purchase #4	$9.53	13.732%	$10.8387	$10.84	$10.85	$10.80
Purchase #5	$241.68	5.520%	$255.0207	$255.02	$255.00	$255.00
Purchase #6	$90.46	12.864%	$102.0968	$102.10	$102.10	$102.10
Purchase #7	$247.70	3.433%	$256.2035	$256.20	$256.20	$256.20
7 purchase totals =	$983.11		$1,041.6565	$1,041.65	$1,041.60	$1,041.60