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	$229.36	5.509%	$241.9954	$242.00	$242.00	$242.00
Purchase #2	$212.49	4.328%	$221.6866	$221.69	$221.70	$221.70
Purchase #3	$80.39	3.766%	$83.4175	$83.42	$83.40	$83.40
Purchase #4	$83.96	5.431%	$88.5199	$88.52	$88.50	$88.50
Purchase #5	$119.85	3.131%	$123.6025	$123.60	$123.60	$123.60
Purchase #6	$113.80	12.500%	$128.025	$128.03	$128.05	$128.00
Purchase #7	$11.87	12.495%	$13.3532	$13.35	$13.35	$13.40
7 purchase totals =	$851.72		$900.6001	$900.61	$900.60	$900.60