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	$12.70	7.512%	$13.654	$13.65	$13.65	$13.70
Purchase #2	$117.84	11.420%	$131.2973	$131.30	$131.30	$131.30
Purchase #3	$202.93	6.786%	$216.7008	$216.70	$216.70	$216.70
Purchase #4	$198.68	5.724%	$210.0524	$210.05	$210.05	$210.10
Purchase #5	$230.82	10.544%	$255.1577	$255.16	$255.15	$255.20
Purchase #6	$97.54	3.155%	$100.6174	$100.62	$100.60	$100.60
Purchase #7	$68.80	4.151%	$71.6559	$71.66	$71.65	$71.70
7 purchase totals =	$929.31		$999.1355	$999.14	$999.10	$999.30