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	$156.29	12.698%	$176.1357	$176.14	$176.15	$176.10
Purchase #2	$21.74	11.321%	$24.2012	$24.20	$24.20	$24.20
Purchase #3	$109.57	12.402%	$123.1589	$123.16	$123.15	$123.20
Purchase #4	$79.75	12.373%	$89.6175	$89.62	$89.60	$89.60
Purchase #5	$47.58	5.204%	$50.0561	$50.06	$50.05	$50.10
Purchase #6	$42.72	12.528%	$48.072	$48.07	$48.05	$48.10
Purchase #7	$51.84	4.332%	$54.0857	$54.09	$54.10	$54.10
7 purchase totals =	$509.49		$565.3271	$565.34	$565.30	$565.40