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	$57.30	4.584%	$59.9266	$59.93	$59.95	$59.90
Purchase #2	$166.28	12.719%	$187.4292	$187.43	$187.45	$187.40
Purchase #3	$172.30	11.155%	$191.5201	$191.52	$191.50	$191.50
Purchase #4	$123.84	11.226%	$137.7423	$137.74	$137.75	$137.70
Purchase #5	$121.67	6.618%	$129.7221	$129.72	$129.70	$129.70
Purchase #6	$134.38	12.323%	$150.9396	$150.94	$150.95	$150.90
Purchase #7	$111.35	9.359%	$121.7712	$121.77	$121.75	$121.80
7 purchase totals =	$887.12		$979.0511	$979.05	$979.05	$978.90