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	$19.35	7.456%	$20.7927	$20.79	$20.80	$20.80
Purchase #2	$118.29	8.566%	$128.4227	$128.42	$128.40	$128.40
Purchase #3	$75.27	3.421%	$77.845	$77.85	$77.85	$77.80
Purchase #4	$119.92	6.871%	$128.1597	$128.16	$128.15	$128.20
Purchase #5	$201.94	13.472%	$229.1454	$229.15	$229.15	$229.10
Purchase #6	$47.31	10.751%	$52.3963	$52.40	$52.40	$52.40
Purchase #7	$30.44	5.304%	$32.0545	$32.05	$32.05	$32.10
7 purchase totals =	$612.52		$668.8163	$668.82	$668.80	$668.80