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	$78.83	6.442%	$83.9082	$83.91	$83.90	$83.90
Purchase #2	$196.70	4.472%	$205.4964	$205.50	$205.50	$205.50
Purchase #3	$137.59	3.186%	$141.9736	$141.97	$141.95	$142.00
Purchase #4	$228.75	4.128%	$238.1928	$238.19	$238.20	$238.20
Purchase #5	$49.72	6.433%	$52.9185	$52.92	$52.90	$52.90
Purchase #6	$71.79	12.260%	$80.5915	$80.59	$80.60	$80.60
Purchase #7	$145.59	5.398%	$153.4489	$153.45	$153.45	$153.40
7 purchase totals =	$908.97		$956.5299	$956.53	$956.50	$956.50