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	$205.79	12.436%	$231.382	$231.38	$231.40	$231.40
Purchase #2	$117.78	11.431%	$131.2434	$131.24	$131.25	$131.20
Purchase #3	$242.35	3.753%	$251.4454	$251.45	$251.45	$251.40
Purchase #4	$18.78	12.290%	$21.0881	$21.09	$21.10	$21.10
Purchase #5	$41.81	4.838%	$43.8328	$43.83	$43.85	$43.80
Purchase #6	$242.67	3.417%	$250.962	$250.96	$250.95	$251.00
Purchase #7	$46.67	7.734%	$50.2795	$50.28	$50.30	$50.30
7 purchase totals =	$915.85		$980.2332	$980.23	$980.30	$980.20