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	$212.27	12.739%	$239.3111	$239.31	$239.30	$239.30
Purchase #2	$117.76	10.758%	$130.4286	$130.43	$130.45	$130.40
Purchase #3	$101.59	12.806%	$114.5996	$114.60	$114.60	$114.60
Purchase #4	$111.81	10.845%	$123.9358	$123.94	$123.95	$123.90
Purchase #5	$45.56	5.157%	$47.9095	$47.91	$47.90	$47.90
Purchase #6	$247.36	9.580%	$271.0571	$271.06	$271.05	$271.10
Purchase #7	$180.52	3.728%	$187.2498	$187.25	$187.25	$187.20
7 purchase totals =	$1,016.87		$1,114.4915	$1,114.50	$1,114.50	$1,114.40