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	$21.81	8.617%	$23.6894	$23.69	$23.70	$23.70
Purchase #2	$24.37	6.343%	$25.9158	$25.92	$25.90	$25.90
Purchase #3	$49.64	11.247%	$55.223	$55.22	$55.20	$55.20
Purchase #4	$248.86	13.239%	$281.8066	$281.81	$281.80	$281.80
Purchase #5	$11.96	5.256%	$12.5886	$12.59	$12.60	$12.60
Purchase #6	$51.30	10.857%	$56.8696	$56.87	$56.85	$56.90
Purchase #7	$38.85	10.409%	$42.8939	$42.89	$42.90	$42.90
7 purchase totals =	$446.79		$498.9869	$498.99	$498.95	$499.00