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	$32.28	13.667%	$36.6917	$36.69	$36.70	$36.70
Purchase #2	$60.30	8.442%	$65.3905	$65.39	$65.40	$65.40
Purchase #3	$88.94	11.824%	$99.4563	$99.46	$99.45	$99.50
Purchase #4	$66.59	4.254%	$69.4227	$69.42	$69.40	$69.40
Purchase #5	$236.88	7.769%	$255.2832	$255.28	$255.30	$255.30
Purchase #6	$58.78	12.869%	$66.3444	$66.34	$66.35	$66.30
Purchase #7	$42.90	7.149%	$45.9669	$45.97	$45.95	$46.00
7 purchase totals =	$586.67		$638.5557	$638.55	$638.55	$638.60