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	$37.55	10.768%	$41.5934	$41.59	$41.60	$41.60
Purchase #2	$145.68	11.308%	$162.1535	$162.15	$162.15	$162.20
Purchase #3	$183.83	4.838%	$192.7237	$192.72	$192.70	$192.70
Purchase #4	$196.85	4.301%	$205.3165	$205.32	$205.30	$205.30
Purchase #5	$17.31	8.742%	$18.8232	$18.82	$18.80	$18.80
Purchase #6	$234.68	12.289%	$263.5198	$263.52	$263.50	$263.50
Purchase #7	$102.37	3.203%	$105.6489	$105.65	$105.65	$105.60
7 purchase totals =	$918.27		$989.7790	$989.77	$989.70	$989.70