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	$113.34	13.491%	$128.6307	$128.63	$128.65	$128.60
Purchase #2	$100.49	10.654%	$111.1962	$111.20	$111.20	$111.20
Purchase #3	$11.27	12.178%	$12.6425	$12.64	$12.65	$12.60
Purchase #4	$133.29	7.139%	$142.8056	$142.81	$142.80	$142.80
Purchase #5	$219.94	3.580%	$227.8139	$227.81	$227.80	$227.80
Purchase #6	$102.25	9.272%	$111.7306	$111.73	$111.75	$111.70
Purchase #7	$240.51	7.251%	$257.9494	$257.95	$257.95	$257.90
7 purchase totals =	$921.09		$992.7689	$992.77	$992.80	$992.60