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	$128.94	10.107%	$141.972	$141.97	$141.95	$142.00
Purchase #2	$43.60	11.522%	$48.6236	$48.62	$48.60	$48.60
Purchase #3	$45.81	13.113%	$51.8171	$51.82	$51.80	$51.80
Purchase #4	$30.33	8.505%	$32.9096	$32.91	$32.90	$32.90
Purchase #5	$224.87	5.766%	$237.836	$237.84	$237.85	$237.80
Purchase #6	$36.31	10.367%	$40.0743	$40.07	$40.05	$40.10
Purchase #7	$107.70	5.356%	$113.4684	$113.47	$113.45	$113.50
7 purchase totals =	$617.56		$666.7010	$666.70	$666.60	$666.70