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	$24.42	12.825%	$27.5519	$27.55	$27.55	$27.60
Purchase #2	$215.30	5.230%	$226.5602	$226.56	$226.55	$226.60
Purchase #3	$116.77	5.500%	$123.1924	$123.19	$123.20	$123.20
Purchase #4	$108.73	4.803%	$113.9523	$113.95	$113.95	$114.00
Purchase #5	$185.74	4.770%	$194.5998	$194.60	$194.60	$194.60
Purchase #6	$61.71	7.797%	$66.5215	$66.52	$66.50	$66.50
Purchase #7	$231.87	10.153%	$255.4118	$255.41	$255.40	$255.40
7 purchase totals =	$944.54		$1,007.7899	$1,007.78	$1,007.75	$1,007.90