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	$150.35	10.838%	$166.6449	$166.64	$166.65	$166.60
Purchase #2	$92.25	13.728%	$104.9141	$104.91	$104.90	$104.90
Purchase #3	$187.30	4.868%	$196.4178	$196.42	$196.40	$196.40
Purchase #4	$142.90	13.407%	$162.0586	$162.06	$162.05	$162.10
Purchase #5	$102.82	4.816%	$107.7718	$107.77	$107.75	$107.80
Purchase #6	$165.80	6.747%	$176.9865	$176.99	$177.00	$177.00
Purchase #7	$53.47	4.804%	$56.0387	$56.04	$56.05	$56.00
7 purchase totals =	$894.89		$970.8324	$970.83	$970.80	$970.80