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	$82.81	7.500%	$89.0208	$89.02	$89.00	$89.00
Purchase #2	$158.72	9.463%	$173.7397	$173.74	$173.75	$173.70
Purchase #3	$169.51	12.473%	$190.653	$190.65	$190.65	$190.70
Purchase #4	$85.84	5.615%	$90.6599	$90.66	$90.65	$90.70
Purchase #5	$136.68	12.466%	$153.7185	$153.72	$153.70	$153.70
Purchase #6	$52.94	10.779%	$58.6464	$58.65	$58.65	$58.60
Purchase #7	$19.52	11.592%	$21.7828	$21.78	$21.80	$21.80
7 purchase totals =	$706.02		$778.2211	$778.22	$778.20	$778.20