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	$151.49	10.503%	$167.401	$167.40	$167.40	$167.40
Purchase #2	$122.61	7.449%	$131.7432	$131.74	$131.75	$131.70
Purchase #3	$54.41	3.836%	$56.4972	$56.50	$56.50	$56.50
Purchase #4	$82.67	5.460%	$87.1838	$87.18	$87.20	$87.20
Purchase #5	$81.71	13.592%	$92.816	$92.82	$92.80	$92.80
Purchase #6	$90.77	13.291%	$102.8342	$102.83	$102.85	$102.80
Purchase #7	$31.78	5.779%	$33.6166	$33.62	$33.60	$33.60
7 purchase totals =	$615.44		$672.0920	$672.09	$672.10	$672.00