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	$162.99	12.513%	$183.3849	$183.38	$183.40	$183.40
Purchase #2	$20.30	12.634%	$22.8647	$22.86	$22.85	$22.90
Purchase #3	$104.71	13.190%	$118.5212	$118.52	$118.50	$118.50
Purchase #4	$63.73	13.161%	$72.1175	$72.12	$72.10	$72.10
Purchase #5	$107.59	4.238%	$112.1497	$112.15	$112.15	$112.10
Purchase #6	$164.76	4.680%	$172.4708	$172.47	$172.45	$172.50
Purchase #7	$196.98	3.596%	$204.0634	$204.06	$204.05	$204.10
7 purchase totals =	$821.06		$885.5722	$885.56	$885.50	$885.60