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	$73.64	10.758%	$81.5622	$81.56	$81.55	$81.60
Purchase #2	$151.45	11.287%	$168.5442	$168.54	$168.55	$168.50
Purchase #3	$160.73	13.158%	$181.8789	$181.88	$181.90	$181.90
Purchase #4	$89.98	10.108%	$99.0752	$99.08	$99.10	$99.10
Purchase #5	$233.85	11.176%	$259.9851	$259.99	$260.00	$260.00
Purchase #6	$158.35	6.582%	$168.7726	$168.77	$168.75	$168.80
Purchase #7	$231.81	7.167%	$248.4238	$248.42	$248.40	$248.40
7 purchase totals =	$1,099.81		$1,208.2420	$1,208.24	$1,208.25	$1,208.30