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	$202.54	10.245%	$223.2902	$223.29	$223.30	$223.30
Purchase #2	$47.98	4.254%	$50.0211	$50.02	$50.00	$50.00
Purchase #3	$139.35	10.452%	$153.9149	$153.91	$153.90	$153.90
Purchase #4	$38.97	8.211%	$42.1698	$42.17	$42.15	$42.20
Purchase #5	$121.25	5.511%	$127.9321	$127.93	$127.95	$127.90
Purchase #6	$124.76	12.714%	$140.622	$140.62	$140.60	$140.60
Purchase #7	$133.36	13.636%	$151.545	$151.55	$151.55	$151.50
7 purchase totals =	$808.21		$889.4951	$889.49	$889.45	$889.40