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	$35.66	13.568%	$40.4983	$40.50	$40.50	$40.50
Purchase #2	$170.75	4.747%	$178.8555	$178.86	$178.85	$178.90
Purchase #3	$104.84	6.108%	$111.2436	$111.24	$111.25	$111.20
Purchase #4	$173.78	3.451%	$179.7771	$179.78	$179.80	$179.80
Purchase #5	$108.33	5.395%	$114.1744	$114.17	$114.15	$114.20
Purchase #6	$123.89	8.351%	$134.2361	$134.24	$134.25	$134.20
Purchase #7	$38.52	10.154%	$42.4313	$42.43	$42.45	$42.40
7 purchase totals =	$755.77		$801.2163	$801.22	$801.25	$801.20