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	$247.65	9.184%	$270.3942	$270.39	$270.40	$270.40
Purchase #2	$83.43	8.680%	$90.6717	$90.67	$90.65	$90.70
Purchase #3	$121.62	10.505%	$134.3962	$134.40	$134.40	$134.40
Purchase #4	$53.75	6.337%	$57.1561	$57.16	$57.15	$57.20
Purchase #5	$230.70	7.579%	$248.1848	$248.18	$248.20	$248.20
Purchase #6	$158.45	13.221%	$179.3987	$179.40	$179.40	$179.40
Purchase #7	$155.43	3.359%	$160.6509	$160.65	$160.65	$160.70
7 purchase totals =	$1,051.03		$1,140.8526	$1,140.85	$1,140.85	$1,141.00