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	$129.94	5.547%	$137.1478	$137.15	$137.15	$137.10
Purchase #2	$103.33	13.257%	$117.0285	$117.03	$117.05	$117.00
Purchase #3	$191.37	9.711%	$209.9539	$209.95	$209.95	$210.00
Purchase #4	$103.25	8.262%	$111.7805	$111.78	$111.80	$111.80
Purchase #5	$84.55	5.834%	$89.4826	$89.48	$89.50	$89.50
Purchase #6	$56.52	10.568%	$62.493	$62.49	$62.50	$62.50
Purchase #7	$74.36	11.373%	$82.817	$82.82	$82.80	$82.80
7 purchase totals =	$743.32		$810.7033	$810.70	$810.75	$810.70