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	$221.29	6.863%	$236.4771	$236.48	$236.50	$236.50
Purchase #2	$29.74	9.588%	$32.5915	$32.59	$32.60	$32.60
Purchase #3	$138.56	8.535%	$150.3861	$150.39	$150.40	$150.40
Purchase #4	$118.92	10.686%	$131.6278	$131.63	$131.65	$131.60
Purchase #5	$94.25	9.323%	$103.0369	$103.04	$103.05	$103.00
Purchase #6	$190.75	9.377%	$208.6366	$208.64	$208.65	$208.60
Purchase #7	$101.35	7.370%	$108.8195	$108.82	$108.80	$108.80
7 purchase totals =	$894.86		$971.5755	$971.59	$971.65	$971.50