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	$161.49	11.287%	$179.7174	$179.72	$179.70	$179.70
Purchase #2	$10.46	6.475%	$11.1373	$11.14	$11.15	$11.10
Purchase #3	$239.89	13.339%	$271.8889	$271.89	$271.90	$271.90
Purchase #4	$81.33	4.235%	$84.7743	$84.77	$84.75	$84.80
Purchase #5	$43.72	10.299%	$48.2227	$48.22	$48.20	$48.20
Purchase #6	$50.85	9.854%	$55.8608	$55.86	$55.85	$55.90
Purchase #7	$138.43	4.687%	$144.9182	$144.92	$144.90	$144.90
7 purchase totals =	$726.17		$796.5196	$796.52	$796.45	$796.50