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	$50.66	6.780%	$54.0947	$54.09	$54.10	$54.10
Purchase #2	$69.94	12.292%	$78.537	$78.54	$78.55	$78.50
Purchase #3	$235.42	8.715%	$255.9369	$255.94	$255.95	$255.90
Purchase #4	$128.32	3.352%	$132.6213	$132.62	$132.60	$132.60
Purchase #5	$12.37	5.506%	$13.0511	$13.05	$13.05	$13.10
Purchase #6	$33.94	13.407%	$38.4903	$38.49	$38.50	$38.50
Purchase #7	$99.33	13.743%	$112.9809	$112.98	$113.00	$113.00
7 purchase totals =	$629.98		$685.7122	$685.71	$685.75	$685.70