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	$10.32	12.501%	$11.6101	$11.61	$11.60	$11.60
Purchase #2	$210.27	12.623%	$236.8124	$236.81	$236.80	$236.80
Purchase #3	$94.51	9.304%	$103.3032	$103.30	$103.30	$103.30
Purchase #4	$18.79	13.611%	$21.3475	$21.35	$21.35	$21.30
Purchase #5	$116.74	12.218%	$131.0033	$131.00	$131.00	$131.00
Purchase #6	$223.42	7.764%	$240.7663	$240.77	$240.75	$240.80
Purchase #7	$199.86	12.374%	$224.5907	$224.59	$224.60	$224.60
7 purchase totals =	$873.91		$969.4335	$969.43	$969.40	$969.40