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	$33.68	12.589%	$37.92	$37.92	$37.90	$37.90
Purchase #2	$123.75	8.277%	$133.9928	$133.99	$134.00	$134.00
Purchase #3	$44.50	6.258%	$47.2848	$47.28	$47.30	$47.30
Purchase #4	$113.31	12.534%	$127.5123	$127.51	$127.50	$127.50
Purchase #5	$107.42	3.820%	$111.5234	$111.52	$111.50	$111.50
Purchase #6	$225.97	13.496%	$256.4669	$256.47	$256.45	$256.50
Purchase #7	$198.43	3.174%	$204.7282	$204.73	$204.75	$204.70
7 purchase totals =	$847.06		$919.4284	$919.42	$919.40	$919.40