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	$9.36	10.198%	$10.3145	$10.31	$10.30	$10.30
Purchase #2	$108.40	3.149%	$111.8135	$111.81	$111.80	$111.80
Purchase #3	$24.51	10.423%	$27.0647	$27.06	$27.05	$27.10
Purchase #4	$200.48	13.784%	$228.1142	$228.11	$228.10	$228.10
Purchase #5	$40.50	6.609%	$43.1766	$43.18	$43.20	$43.20
Purchase #6	$22.75	12.565%	$25.6085	$25.61	$25.60	$25.60
Purchase #7	$106.55	11.511%	$118.815	$118.82	$118.80	$118.80
7 purchase totals =	$512.55		$564.9070	$564.90	$564.85	$564.90