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	$70.31	12.184%	$78.8766	$78.88	$78.90	$78.90
Purchase #2	$168.65	10.440%	$186.2571	$186.26	$186.25	$186.30
Purchase #3	$116.69	10.468%	$128.9051	$128.91	$128.90	$128.90
Purchase #4	$49.32	10.652%	$54.5736	$54.57	$54.55	$54.60
Purchase #5	$16.83	4.127%	$17.5246	$17.52	$17.50	$17.50
Purchase #6	$146.74	8.185%	$158.7507	$158.75	$158.75	$158.80
Purchase #7	$145.83	5.171%	$153.3709	$153.37	$153.35	$153.40
7 purchase totals =	$714.37		$778.2586	$778.26	$778.20	$778.40