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	$20.55	4.805%	$21.5374	$21.54	$21.55	$21.50
Purchase #2	$134.97	13.745%	$153.5216	$153.52	$153.50	$153.50
Purchase #3	$135.30	6.332%	$143.8672	$143.87	$143.85	$143.90
Purchase #4	$74.88	10.523%	$82.7596	$82.76	$82.75	$82.80
Purchase #5	$121.70	10.108%	$134.0014	$134.00	$134.00	$134.00
Purchase #6	$104.75	12.789%	$118.1465	$118.15	$118.15	$118.10
Purchase #7	$74.57	9.384%	$81.5676	$81.57	$81.55	$81.60
7 purchase totals =	$666.72		$735.4013	$735.41	$735.35	$735.40