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	$128.35	12.649%	$144.585	$144.59	$144.60	$144.60
Purchase #2	$62.61	5.182%	$65.8545	$65.85	$65.85	$65.90
Purchase #3	$98.90	5.188%	$104.0309	$104.03	$104.05	$104.00
Purchase #4	$7.78	13.751%	$8.8498	$8.85	$8.85	$8.80
Purchase #5	$127.52	5.195%	$134.1447	$134.14	$134.15	$134.10
Purchase #6	$42.92	5.226%	$45.163	$45.16	$45.15	$45.20
Purchase #7	$139.96	3.485%	$144.8376	$144.84	$144.85	$144.80
7 purchase totals =	$608.04		$647.4655	$647.46	$647.50	$647.40