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	$9.94	6.573%	$10.5934	$10.59	$10.60	$10.60
Purchase #2	$19.32	9.866%	$21.2261	$21.23	$21.25	$21.20
Purchase #3	$78.25	13.122%	$88.518	$88.52	$88.50	$88.50
Purchase #4	$43.92	4.498%	$45.8955	$45.90	$45.90	$45.90
Purchase #5	$126.92	5.519%	$133.9247	$133.92	$133.90	$133.90
Purchase #6	$108.91	3.615%	$112.8471	$112.85	$112.85	$112.80
Purchase #7	$130.59	13.605%	$148.3568	$148.36	$148.35	$148.40
7 purchase totals =	$517.85		$561.3616	$561.37	$561.35	$561.30