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	$74.89	10.596%	$82.8253	$82.83	$82.85	$82.80
Purchase #2	$107.80	6.812%	$115.1433	$115.14	$115.15	$115.10
Purchase #3	$121.79	8.259%	$131.8486	$131.85	$131.85	$131.80
Purchase #4	$39.81	9.225%	$43.4825	$43.48	$43.50	$43.50
Purchase #5	$96.85	8.506%	$105.0881	$105.09	$105.10	$105.10
Purchase #6	$52.91	3.255%	$54.6322	$54.63	$54.65	$54.60
Purchase #7	$13.89	6.452%	$14.7862	$14.79	$14.80	$14.80
7 purchase totals =	$507.94		$547.8062	$547.81	$547.90	$547.70