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	$49.90	5.829%	$52.8087	$52.81	$52.80	$52.80
Purchase #2	$234.97	6.651%	$250.5979	$250.60	$250.60	$250.60
Purchase #3	$148.47	8.409%	$160.9548	$160.95	$160.95	$161.00
Purchase #4	$102.64	5.720%	$108.511	$108.51	$108.50	$108.50
Purchase #5	$31.45	12.681%	$35.4382	$35.44	$35.45	$35.40
Purchase #6	$233.86	9.291%	$255.5879	$255.59	$255.60	$255.60
Purchase #7	$138.96	6.451%	$147.9243	$147.92	$147.90	$147.90
7 purchase totals =	$940.25		$1,011.8228	$1,011.82	$1,011.80	$1,011.80