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	$127.56	13.277%	$144.4961	$144.50	$144.50	$144.50
Purchase #2	$109.95	4.115%	$114.4744	$114.47	$114.45	$114.50
Purchase #3	$144.52	12.544%	$162.6486	$162.65	$162.65	$162.60
Purchase #4	$153.85	12.390%	$172.912	$172.91	$172.90	$172.90
Purchase #5	$212.59	4.229%	$221.5804	$221.58	$221.60	$221.60
Purchase #6	$215.79	12.228%	$242.1768	$242.18	$242.20	$242.20
Purchase #7	$71.42	10.172%	$78.6848	$78.68	$78.70	$78.70
7 purchase totals =	$1,035.68		$1,136.9731	$1,136.97	$1,137.00	$1,137.00