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	$149.71	5.705%	$158.251	$158.25	$158.25	$158.30
Purchase #2	$177.39	10.661%	$196.3015	$196.30	$196.30	$196.30
Purchase #3	$134.58	3.746%	$139.6214	$139.62	$139.60	$139.60
Purchase #4	$107.82	5.403%	$113.6455	$113.65	$113.65	$113.60
Purchase #5	$149.60	13.388%	$169.6284	$169.63	$169.65	$169.60
Purchase #6	$98.70	4.321%	$102.9648	$102.96	$102.95	$103.00
Purchase #7	$100.29	3.232%	$103.5314	$103.53	$103.55	$103.50
7 purchase totals =	$918.09		$983.9440	$983.94	$983.95	$983.90