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	$234.72	12.263%	$263.5037	$263.50	$263.50	$263.50
Purchase #2	$173.99	8.383%	$188.5756	$188.58	$188.60	$188.60
Purchase #3	$89.75	12.150%	$100.6546	$100.65	$100.65	$100.70
Purchase #4	$7.61	3.508%	$7.877	$7.88	$7.90	$7.90
Purchase #5	$132.86	11.397%	$148.0021	$148.00	$148.00	$148.00
Purchase #6	$105.61	12.320%	$118.6212	$118.62	$118.60	$118.60
Purchase #7	$14.30	10.528%	$15.8055	$15.81	$15.80	$15.80
7 purchase totals =	$758.84		$843.0397	$843.04	$843.05	$843.10