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	$112.59	13.490%	$127.7784	$127.78	$127.80	$127.80
Purchase #2	$48.55	13.269%	$54.9921	$54.99	$55.00	$55.00
Purchase #3	$247.45	12.193%	$277.6216	$277.62	$277.60	$277.60
Purchase #4	$89.51	13.321%	$101.4336	$101.43	$101.45	$101.40
Purchase #5	$65.38	9.796%	$71.7846	$71.78	$71.80	$71.80
Purchase #6	$175.72	10.300%	$193.8192	$193.82	$193.80	$193.80
Purchase #7	$76.70	8.283%	$83.0531	$83.05	$83.05	$83.10
7 purchase totals =	$815.90		$910.4826	$910.47	$910.50	$910.50