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	$224.47	13.659%	$255.1304	$255.13	$255.15	$255.10
Purchase #2	$15.43	10.509%	$17.0515	$17.05	$17.05	$17.10
Purchase #3	$118.38	13.221%	$134.031	$134.03	$134.05	$134.00
Purchase #4	$149.26	6.202%	$158.5171	$158.52	$158.50	$158.50
Purchase #5	$106.31	6.239%	$112.9427	$112.94	$112.95	$112.90
Purchase #6	$34.30	9.382%	$37.518	$37.52	$37.50	$37.50
Purchase #7	$104.45	6.515%	$111.2549	$111.25	$111.25	$111.30
7 purchase totals =	$752.60		$826.4456	$826.44	$826.45	$826.40