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	$230.39	8.290%	$249.4893	$249.49	$249.50	$249.50
Purchase #2	$164.45	5.591%	$173.6444	$173.64	$173.65	$173.60
Purchase #3	$183.66	12.332%	$206.309	$206.31	$206.30	$206.30
Purchase #4	$31.79	6.719%	$33.926	$33.93	$33.95	$33.90
Purchase #5	$108.59	8.298%	$117.6008	$117.60	$117.60	$117.60
Purchase #6	$145.67	13.782%	$165.7462	$165.75	$165.75	$165.70
Purchase #7	$105.39	5.412%	$111.0937	$111.09	$111.10	$111.10
7 purchase totals =	$969.94		$1,057.8094	$1,057.81	$1,057.85	$1,057.70