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	$235.93	8.754%	$256.5833	$256.58	$256.60	$256.60
Purchase #2	$37.30	7.749%	$40.1904	$40.19	$40.20	$40.20
Purchase #3	$30.85	3.616%	$31.9655	$31.97	$31.95	$32.00
Purchase #4	$133.26	7.261%	$142.936	$142.94	$142.95	$142.90
Purchase #5	$230.32	6.311%	$244.8555	$244.86	$244.85	$244.90
Purchase #6	$246.45	11.572%	$274.9692	$274.97	$274.95	$275.00
Purchase #7	$105.70	5.762%	$111.7904	$111.79	$111.80	$111.80
7 purchase totals =	$1,019.81		$1,103.2903	$1,103.30	$1,103.30	$1,103.40