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	$100.87	10.550%	$111.5118	$111.51	$111.50	$111.50
Purchase #2	$85.69	4.571%	$89.6069	$89.61	$89.60	$89.60
Purchase #3	$12.37	5.461%	$13.0455	$13.05	$13.05	$13.00
Purchase #4	$173.81	7.117%	$186.1801	$186.18	$186.20	$186.20
Purchase #5	$153.87	13.609%	$174.8102	$174.81	$174.80	$174.80
Purchase #6	$127.62	11.210%	$141.9262	$141.93	$141.95	$141.90
Purchase #7	$132.78	6.169%	$140.9712	$140.97	$140.95	$141.00
7 purchase totals =	$787.01		$858.0519	$858.06	$858.05	$858.00