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	$63.70	3.421%	$65.8792	$65.88	$65.90	$65.90
Purchase #2	$52.83	8.136%	$57.1282	$57.13	$57.15	$57.10
Purchase #3	$148.88	4.139%	$155.0421	$155.04	$155.05	$155.00
Purchase #4	$238.42	5.202%	$250.8226	$250.82	$250.80	$250.80
Purchase #5	$61.99	8.861%	$67.4829	$67.48	$67.50	$67.50
Purchase #6	$51.60	13.536%	$58.5846	$58.58	$58.60	$58.60
Purchase #7	$34.25	3.588%	$35.4789	$35.48	$35.50	$35.50
7 purchase totals =	$651.67		$690.4185	$690.41	$690.50	$690.40