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	$171.27	5.384%	$180.4912	$180.49	$180.50	$180.50
Purchase #2	$188.69	4.620%	$197.4075	$197.41	$197.40	$197.40
Purchase #3	$34.30	9.604%	$37.5942	$37.59	$37.60	$37.60
Purchase #4	$97.82	13.706%	$111.2272	$111.23	$111.25	$111.20
Purchase #5	$152.84	7.331%	$164.0447	$164.04	$164.05	$164.00
Purchase #6	$131.45	5.302%	$138.4195	$138.42	$138.40	$138.40
Purchase #7	$91.34	9.857%	$100.3434	$100.34	$100.35	$100.30
7 purchase totals =	$867.71		$929.5277	$929.52	$929.55	$929.40