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	$24.50	13.743%	$27.867	$27.87	$27.85	$27.90
Purchase #2	$19.35	3.718%	$20.0694	$20.07	$20.05	$20.10
Purchase #3	$9.45	9.858%	$10.3816	$10.38	$10.40	$10.40
Purchase #4	$103.88	7.514%	$111.6855	$111.69	$111.70	$111.70
Purchase #5	$119.42	11.173%	$132.7628	$132.76	$132.75	$132.80
Purchase #6	$210.53	6.587%	$224.3976	$224.40	$224.40	$224.40
Purchase #7	$148.77	11.804%	$166.3308	$166.33	$166.35	$166.30
7 purchase totals =	$635.90		$693.4947	$693.50	$693.50	$693.60