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	$247.99	11.672%	$276.9354	$276.94	$276.95	$276.90
Purchase #2	$174.45	8.599%	$189.451	$189.45	$189.45	$189.50
Purchase #3	$184.49	6.513%	$196.5058	$196.51	$196.50	$196.50
Purchase #4	$38.66	5.708%	$40.8667	$40.87	$40.85	$40.90
Purchase #5	$5.54	13.795%	$6.3042	$6.30	$6.30	$6.30
Purchase #6	$136.66	11.233%	$152.011	$152.01	$152.00	$152.00
Purchase #7	$163.30	8.263%	$176.7935	$176.79	$176.80	$176.80
7 purchase totals =	$951.09		$1,038.8676	$1,038.87	$1,038.85	$1,038.90