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	$159.46	3.801%	$165.5211	$165.52	$165.50	$165.50
Purchase #2	$118.96	4.158%	$123.9064	$123.91	$123.90	$123.90
Purchase #3	$240.91	5.510%	$254.1841	$254.18	$254.20	$254.20
Purchase #4	$173.81	4.529%	$181.6819	$181.68	$181.70	$181.70
Purchase #5	$127.42	5.813%	$134.8269	$134.83	$134.85	$134.80
Purchase #6	$197.96	9.421%	$216.6098	$216.61	$216.60	$216.60
Purchase #7	$215.63	10.701%	$238.7046	$238.70	$238.70	$238.70
7 purchase totals =	$1,234.15		$1,315.4348	$1,315.43	$1,315.45	$1,315.40