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	$153.70	9.810%	$168.778	$168.78	$168.80	$168.80
Purchase #2	$199.82	12.250%	$224.298	$224.30	$224.30	$224.30
Purchase #3	$35.59	8.424%	$38.5881	$38.59	$38.60	$38.60
Purchase #4	$118.80	10.616%	$131.4118	$131.41	$131.40	$131.40
Purchase #5	$104.80	6.691%	$111.8122	$111.81	$111.80	$111.80
Purchase #6	$91.86	13.730%	$104.4724	$104.47	$104.45	$104.50
Purchase #7	$8.72	9.592%	$9.5564	$9.56	$9.55	$9.60
7 purchase totals =	$713.29		$788.9169	$788.92	$788.90	$789.00