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	$6.90	13.609%	$7.839	$7.84	$7.85	$7.80
Purchase #2	$135.57	7.581%	$145.8476	$145.85	$145.85	$145.80
Purchase #3	$54.98	13.698%	$62.5112	$62.51	$62.50	$62.50
Purchase #4	$247.44	9.823%	$271.746	$271.75	$271.75	$271.70
Purchase #5	$60.36	10.306%	$66.5807	$66.58	$66.60	$66.60
Purchase #6	$184.80	13.774%	$210.2544	$210.25	$210.25	$210.30
Purchase #7	$172.98	13.812%	$196.872	$196.87	$196.85	$196.90
7 purchase totals =	$863.03		$961.6509	$961.65	$961.65	$961.60