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	5.339%	$15.4322	$15.43	$15.45	$15.40
Purchase #2	$229.92	11.506%	$256.3746	$256.37	$256.35	$256.40
Purchase #3	$48.42	7.343%	$51.9755	$51.98	$52.00	$52.00
Purchase #4	$92.76	3.664%	$96.1587	$96.16	$96.15	$96.20
Purchase #5	$48.84	7.497%	$52.5015	$52.50	$52.50	$52.50
Purchase #6	$229.85	12.852%	$259.3903	$259.39	$259.40	$259.40
Purchase #7	$107.46	4.293%	$112.0733	$112.07	$112.05	$112.10
7 purchase totals =	$771.90		$843.9061	$843.90	$843.90	$844.00