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	$123.55	10.576%	$136.6166	$136.62	$136.60	$136.60
Purchase #2	$46.92	7.663%	$50.5155	$50.52	$50.50	$50.50
Purchase #3	$33.61	5.857%	$35.5785	$35.58	$35.60	$35.60
Purchase #4	$20.37	7.547%	$21.9073	$21.91	$21.90	$21.90
Purchase #5	$233.76	12.454%	$262.8725	$262.87	$262.85	$262.90
Purchase #6	$31.56	4.808%	$33.0774	$33.08	$33.10	$33.10
Purchase #7	$92.51	11.720%	$103.3522	$103.35	$103.35	$103.40
7 purchase totals =	$582.28		$643.9200	$643.93	$643.90	$644.00