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	$16.34	8.412%	$17.7145	$17.71	$17.70	$17.70
Purchase #2	$59.81	13.407%	$67.8287	$67.83	$67.85	$67.80
Purchase #3	$197.61	12.536%	$222.3824	$222.38	$222.40	$222.40
Purchase #4	$146.98	4.723%	$153.9219	$153.92	$153.90	$153.90
Purchase #5	$219.49	6.308%	$233.3354	$233.34	$233.35	$233.30
Purchase #6	$156.69	13.871%	$178.4245	$178.42	$178.40	$178.40
Purchase #7	$38.81	7.826%	$41.8473	$41.85	$41.85	$41.80
7 purchase totals =	$835.73		$915.4547	$915.45	$915.45	$915.30