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	$66.49	11.714%	$74.2786	$74.28	$74.30	$74.30
Purchase #2	$194.55	6.819%	$207.8164	$207.82	$207.80	$207.80
Purchase #3	$85.70	5.244%	$90.1941	$90.19	$90.20	$90.20
Purchase #4	$34.34	7.167%	$36.8011	$36.80	$36.80	$36.80
Purchase #5	$226.77	12.672%	$255.5063	$255.51	$255.50	$255.50
Purchase #6	$82.30	10.475%	$90.9209	$90.92	$90.90	$90.90
Purchase #7	$49.71	3.693%	$51.5458	$51.55	$51.55	$51.50
7 purchase totals =	$739.86		$807.0632	$807.07	$807.05	$807.00