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	$144.36	6.786%	$154.1563	$154.16	$154.15	$154.20
Purchase #2	$101.47	10.243%	$111.8636	$111.86	$111.85	$111.90
Purchase #3	$19.43	9.477%	$21.2714	$21.27	$21.25	$21.30
Purchase #4	$179.89	6.823%	$192.1639	$192.16	$192.15	$192.20
Purchase #5	$34.52	8.557%	$37.4739	$37.47	$37.45	$37.50
Purchase #6	$38.30	13.544%	$43.4874	$43.49	$43.50	$43.50
Purchase #7	$238.52	4.814%	$250.0024	$250.00	$250.00	$250.00
7 purchase totals =	$756.49		$810.4189	$810.41	$810.35	$810.60