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	$248.72	13.476%	$282.2375	$282.24	$282.25	$282.20
Purchase #2	$19.32	11.388%	$21.5202	$21.52	$21.50	$21.50
Purchase #3	$105.26	5.754%	$111.3167	$111.32	$111.30	$111.30
Purchase #4	$24.57	7.439%	$26.3978	$26.40	$26.40	$26.40
Purchase #5	$195.39	9.561%	$214.0712	$214.07	$214.05	$214.10
Purchase #6	$146.93	5.800%	$155.4519	$155.45	$155.45	$155.50
Purchase #7	$90.98	13.842%	$103.5735	$103.57	$103.55	$103.60
7 purchase totals =	$831.17		$914.5688	$914.57	$914.50	$914.60