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	$137.96	6.738%	$147.2557	$147.26	$147.25	$147.30
Purchase #2	$169.40	3.820%	$175.8711	$175.87	$175.85	$175.90
Purchase #3	$116.61	12.820%	$131.5594	$131.56	$131.55	$131.60
Purchase #4	$154.59	13.838%	$175.9822	$175.98	$176.00	$176.00
Purchase #5	$5.49	12.105%	$6.1546	$6.15	$6.15	$6.20
Purchase #6	$104.43	7.723%	$112.4951	$112.50	$112.50	$112.50
Purchase #7	$231.94	10.489%	$256.2682	$256.27	$256.25	$256.30
7 purchase totals =	$920.42		$1,005.5863	$1,005.59	$1,005.55	$1,005.80