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	$18.47	5.209%	$19.4321	$19.43	$19.45	$19.40
Purchase #2	$105.38	11.821%	$117.837	$117.84	$117.85	$117.80
Purchase #3	$52.84	8.191%	$57.1681	$57.17	$57.15	$57.20
Purchase #4	$232.68	7.128%	$249.2654	$249.27	$249.25	$249.30
Purchase #5	$18.66	11.816%	$20.8649	$20.86	$20.85	$20.90
Purchase #6	$84.80	7.121%	$90.8386	$90.84	$90.85	$90.80
Purchase #7	$43.67	6.203%	$46.3789	$46.38	$46.40	$46.40
7 purchase totals =	$556.50		$601.7850	$601.79	$601.80	$601.80