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	$48.35	7.249%	$51.8549	$51.85	$51.85	$51.90
Purchase #2	$130.97	5.291%	$137.8996	$137.90	$137.90	$137.90
Purchase #3	$49.56	7.774%	$53.4128	$53.41	$53.40	$53.40
Purchase #4	$198.25	9.323%	$216.7328	$216.73	$216.75	$216.70
Purchase #5	$47.29	10.235%	$52.1301	$52.13	$52.15	$52.10
Purchase #6	$29.98	7.261%	$32.1568	$32.16	$32.15	$32.20
Purchase #7	$214.38	3.829%	$222.5886	$222.59	$222.60	$222.60
7 purchase totals =	$718.78		$766.7756	$766.77	$766.80	$766.80