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	$114.83	12.225%	$128.868	$128.87	$128.85	$128.90
Purchase #2	$214.56	3.543%	$222.1619	$222.16	$222.15	$222.20
Purchase #3	$149.42	6.412%	$159.0008	$159.00	$159.00	$159.00
Purchase #4	$42.88	13.536%	$48.6842	$48.68	$48.70	$48.70
Purchase #5	$118.85	11.535%	$132.5593	$132.56	$132.55	$132.60
Purchase #6	$225.84	5.790%	$238.9161	$238.92	$238.90	$238.90
Purchase #7	$36.38	10.403%	$40.1646	$40.16	$40.15	$40.20
7 purchase totals =	$902.76		$970.3549	$970.35	$970.30	$970.50