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	$19.79	6.534%	$21.0831	$21.08	$21.10	$21.10
Purchase #2	$134.43	3.592%	$139.2587	$139.26	$139.25	$139.30
Purchase #3	$66.75	7.509%	$71.7623	$71.76	$71.75	$71.80
Purchase #4	$111.60	13.538%	$126.7084	$126.71	$126.70	$126.70
Purchase #5	$161.50	10.246%	$178.0473	$178.05	$178.05	$178.00
Purchase #6	$122.46	3.592%	$126.8588	$126.86	$126.85	$126.90
Purchase #7	$37.69	13.770%	$42.8799	$42.88	$42.90	$42.90
7 purchase totals =	$654.22		$706.5985	$706.60	$706.60	$706.70