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	$23.48	11.677%	$26.2218	$26.22	$26.20	$26.20
Purchase #2	$95.55	8.764%	$103.924	$103.92	$103.90	$103.90
Purchase #3	$116.42	13.219%	$131.8096	$131.81	$131.80	$131.80
Purchase #4	$29.62	5.485%	$31.2447	$31.24	$31.25	$31.20
Purchase #5	$132.59	7.413%	$142.4189	$142.42	$142.40	$142.40
Purchase #6	$104.43	13.554%	$118.5844	$118.58	$118.60	$118.60
Purchase #7	$19.76	9.788%	$21.6941	$21.69	$21.70	$21.70
7 purchase totals =	$521.85		$575.8975	$575.88	$575.85	$575.80