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	$157.79	5.589%	$166.6089	$166.61	$166.60	$166.60
Purchase #2	$226.89	8.495%	$246.1643	$246.16	$246.15	$246.20
Purchase #3	$41.33	4.576%	$43.2213	$43.22	$43.20	$43.20
Purchase #4	$96.38	3.855%	$100.0954	$100.10	$100.10	$100.10
Purchase #5	$174.53	4.528%	$182.4327	$182.43	$182.45	$182.40
Purchase #6	$136.97	3.831%	$142.2173	$142.22	$142.20	$142.20
Purchase #7	$101.48	10.312%	$111.9446	$111.94	$111.95	$111.90
7 purchase totals =	$935.37		$992.6845	$992.68	$992.65	$992.60