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	$55.78	6.143%	$59.2066	$59.21	$59.20	$59.20
Purchase #2	$112.49	4.722%	$117.8018	$117.80	$117.80	$117.80
Purchase #3	$48.99	8.487%	$53.1478	$53.15	$53.15	$53.10
Purchase #4	$231.49	13.364%	$262.4263	$262.43	$262.45	$262.40
Purchase #5	$108.71	8.400%	$117.8416	$117.84	$117.85	$117.80
Purchase #6	$105.37	6.434%	$112.1495	$112.15	$112.15	$112.10
Purchase #7	$79.61	3.715%	$82.5675	$82.57	$82.55	$82.60
7 purchase totals =	$742.44		$805.1411	$805.15	$805.15	$805.00