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	$229.49	12.123%	$257.3111	$257.31	$257.30	$257.30
Purchase #2	$187.32	6.285%	$199.0931	$199.09	$199.10	$199.10
Purchase #3	$170.64	7.111%	$182.7742	$182.77	$182.75	$182.80
Purchase #4	$33.48	11.357%	$37.2823	$37.28	$37.30	$37.30
Purchase #5	$216.70	6.123%	$229.9685	$229.97	$229.95	$230.00
Purchase #6	$150.61	13.151%	$170.4167	$170.42	$170.40	$170.40
Purchase #7	$17.83	9.693%	$19.5583	$19.56	$19.55	$19.60
7 purchase totals =	$1,006.07		$1,096.4042	$1,096.40	$1,096.35	$1,096.50