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	$70.46	11.152%	$78.3177	$78.32	$78.30	$78.30
Purchase #2	$150.75	9.714%	$165.3939	$165.39	$165.40	$165.40
Purchase #3	$102.48	5.613%	$108.2322	$108.23	$108.25	$108.20
Purchase #4	$128.45	3.528%	$132.9817	$132.98	$133.00	$133.00
Purchase #5	$90.67	8.454%	$98.3352	$98.34	$98.35	$98.30
Purchase #6	$145.60	3.348%	$150.4747	$150.47	$150.45	$150.50
Purchase #7	$153.77	7.366%	$165.0967	$165.10	$165.10	$165.10
7 purchase totals =	$842.18		$898.8321	$898.83	$898.85	$898.80