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	$93.59	12.810%	$105.5789	$105.58	$105.60	$105.60
Purchase #2	$89.32	6.698%	$95.3027	$95.30	$95.30	$95.30
Purchase #3	$219.76	12.249%	$246.6784	$246.68	$246.70	$246.70
Purchase #4	$57.86	4.566%	$60.5019	$60.50	$60.50	$60.50
Purchase #5	$212.45	12.510%	$239.0275	$239.03	$239.05	$239.00
Purchase #6	$117.87	8.275%	$127.6237	$127.62	$127.60	$127.60
Purchase #7	$92.60	13.659%	$105.2482	$105.25	$105.25	$105.20
7 purchase totals =	$883.45		$979.9613	$979.96	$980.00	$979.90