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	$59.74	11.489%	$66.6035	$66.60	$66.60	$66.60
Purchase #2	$105.52	12.159%	$118.3502	$118.35	$118.35	$118.40
Purchase #3	$125.26	11.328%	$139.4495	$139.45	$139.45	$139.40
Purchase #4	$40.93	3.390%	$42.3175	$42.32	$42.30	$42.30
Purchase #5	$65.55	10.723%	$72.5789	$72.58	$72.60	$72.60
Purchase #6	$183.95	5.381%	$193.8483	$193.85	$193.85	$193.80
Purchase #7	$108.91	9.510%	$119.2673	$119.27	$119.25	$119.30
7 purchase totals =	$689.86		$752.4152	$752.42	$752.40	$752.40