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	$111.71	6.146%	$118.5757	$118.58	$118.60	$118.60
Purchase #2	$125.95	5.229%	$132.5359	$132.54	$132.55	$132.50
Purchase #3	$104.28	9.814%	$114.514	$114.51	$114.50	$114.50
Purchase #4	$61.47	8.221%	$66.5234	$66.52	$66.50	$66.50
Purchase #5	$198.67	10.692%	$219.9118	$219.91	$219.90	$219.90
Purchase #6	$215.78	8.109%	$233.2776	$233.28	$233.30	$233.30
Purchase #7	$110.27	3.400%	$114.0192	$114.02	$114.00	$114.00
7 purchase totals =	$928.13		$999.3576	$999.36	$999.35	$999.30