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	$169.90	12.364%	$190.9064	$190.91	$190.90	$190.90
Purchase #2	$19.97	11.724%	$22.3113	$22.31	$22.30	$22.30
Purchase #3	$81.61	7.188%	$87.4761	$87.48	$87.50	$87.50
Purchase #4	$80.42	6.729%	$85.8315	$85.83	$85.85	$85.80
Purchase #5	$77.40	6.685%	$82.5742	$82.57	$82.55	$82.60
Purchase #6	$179.52	10.817%	$198.9387	$198.94	$198.95	$198.90
Purchase #7	$71.45	4.372%	$74.5738	$74.57	$74.55	$74.60
7 purchase totals =	$680.27		$742.6120	$742.61	$742.60	$742.60