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	$14.65	3.256%	$15.127	$15.13	$15.15	$15.10
Purchase #2	$250.99	12.613%	$282.6474	$282.65	$282.65	$282.60
Purchase #3	$244.31	3.259%	$252.2721	$252.27	$252.25	$252.30
Purchase #4	$192.81	11.510%	$215.0024	$215.00	$215.00	$215.00
Purchase #5	$148.42	11.451%	$165.4156	$165.42	$165.40	$165.40
Purchase #6	$19.89	5.342%	$20.9525	$20.95	$20.95	$21.00
Purchase #7	$179.51	9.285%	$196.1775	$196.18	$196.20	$196.20
7 purchase totals =	$1,050.58		$1,147.5945	$1,147.60	$1,147.60	$1,147.60