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	$78.82	4.584%	$82.4331	$82.43	$82.45	$82.40
Purchase #2	$60.37	6.672%	$64.3979	$64.40	$64.40	$64.40
Purchase #3	$199.63	8.753%	$217.1036	$217.10	$217.10	$217.10
Purchase #4	$35.91	8.826%	$39.0794	$39.08	$39.10	$39.10
Purchase #5	$20.71	4.486%	$21.6391	$21.64	$21.65	$21.60
Purchase #6	$106.72	12.253%	$119.7964	$119.80	$119.80	$119.80
Purchase #7	$104.82	11.161%	$116.519	$116.52	$116.50	$116.50
7 purchase totals =	$606.98		$660.9685	$660.97	$661.00	$660.90