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	$240.77	8.351%	$260.8767	$260.88	$260.90	$260.90
Purchase #2	$53.62	3.272%	$55.3744	$55.37	$55.35	$55.40
Purchase #3	$226.56	13.250%	$256.5792	$256.58	$256.60	$256.60
Purchase #4	$132.47	5.793%	$140.144	$140.14	$140.15	$140.10
Purchase #5	$55.70	13.822%	$63.3989	$63.40	$63.40	$63.40
Purchase #6	$133.66	4.196%	$139.2684	$139.27	$139.25	$139.30
Purchase #7	$165.25	9.860%	$181.5437	$181.54	$181.55	$181.50
7 purchase totals =	$1,008.03		$1,097.1853	$1,097.18	$1,097.20	$1,097.20