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	$189.53	10.119%	$208.7085	$208.71	$208.70	$208.70
Purchase #2	$180.85	7.551%	$194.506	$194.51	$194.50	$194.50
Purchase #3	$117.82	6.604%	$125.6008	$125.60	$125.60	$125.60
Purchase #4	$48.94	11.158%	$54.4007	$54.40	$54.40	$54.40
Purchase #5	$95.38	5.862%	$100.9712	$100.97	$100.95	$101.00
Purchase #6	$208.79	13.730%	$237.4569	$237.46	$237.45	$237.50
Purchase #7	$52.99	7.330%	$56.8742	$56.87	$56.85	$56.90
7 purchase totals =	$894.30		$978.5183	$978.52	$978.45	$978.60