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	$177.57	12.684%	$200.093	$200.09	$200.10	$200.10
Purchase #2	$118.46	13.487%	$134.4367	$134.44	$134.45	$134.40
Purchase #3	$45.46	9.806%	$49.9178	$49.92	$49.90	$49.90
Purchase #4	$72.82	13.592%	$82.7177	$82.72	$82.70	$82.70
Purchase #5	$80.54	6.726%	$85.9571	$85.96	$85.95	$86.00
Purchase #6	$13.57	5.429%	$14.3067	$14.31	$14.30	$14.30
Purchase #7	$74.88	3.261%	$77.3218	$77.32	$77.30	$77.30
7 purchase totals =	$583.30		$644.7508	$644.76	$644.70	$644.70