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	$158.98	5.287%	$167.3853	$167.39	$167.40	$167.40
Purchase #2	$127.84	9.682%	$140.2175	$140.22	$140.20	$140.20
Purchase #3	$18.97	9.755%	$20.8205	$20.82	$20.80	$20.80
Purchase #4	$70.98	13.552%	$80.5992	$80.60	$80.60	$80.60
Purchase #5	$100.37	10.733%	$111.1427	$111.14	$111.15	$111.10
Purchase #6	$71.52	4.111%	$74.4602	$74.46	$74.45	$74.50
Purchase #7	$250.79	12.764%	$282.8008	$282.80	$282.80	$282.80
7 purchase totals =	$799.45		$877.4262	$877.43	$877.40	$877.40