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	$50.71	3.590%	$52.5305	$52.53	$52.55	$52.50
Purchase #2	$226.46	6.435%	$241.0327	$241.03	$241.05	$241.00
Purchase #3	$156.28	9.103%	$170.5062	$170.51	$170.50	$170.50
Purchase #4	$49.35	9.259%	$53.9193	$53.92	$53.90	$53.90
Purchase #5	$31.64	3.737%	$32.8224	$32.82	$32.80	$32.80
Purchase #6	$94.83	12.510%	$106.6932	$106.69	$106.70	$106.70
Purchase #7	$7.52	11.449%	$8.381	$8.38	$8.40	$8.40
7 purchase totals =	$616.79		$665.8853	$665.88	$665.90	$665.80