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	$33.84	12.477%	$38.0622	$38.06	$38.05	$38.10
Purchase #2	$218.34	5.547%	$230.4513	$230.45	$230.45	$230.50
Purchase #3	$120.35	5.699%	$127.2087	$127.21	$127.20	$127.20
Purchase #4	$108.58	5.292%	$114.3261	$114.33	$114.35	$114.30
Purchase #5	$158.44	9.527%	$173.5346	$173.53	$173.55	$173.50
Purchase #6	$47.42	10.533%	$52.4147	$52.41	$52.40	$52.40
Purchase #7	$59.67	5.445%	$62.919	$62.92	$62.90	$62.90
7 purchase totals =	$746.64		$798.9166	$798.91	$798.90	$798.90