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	$149.89	9.204%	$163.6859	$163.69	$163.70	$163.70
Purchase #2	$29.77	11.394%	$33.162	$33.16	$33.15	$33.20
Purchase #3	$56.34	5.811%	$59.6139	$59.61	$59.60	$59.60
Purchase #4	$104.35	4.583%	$109.1324	$109.13	$109.15	$109.10
Purchase #5	$139.72	3.857%	$145.109	$145.11	$145.10	$145.10
Purchase #6	$225.96	13.529%	$256.5301	$256.53	$256.55	$256.50
Purchase #7	$205.77	7.805%	$221.8303	$221.83	$221.85	$221.80
7 purchase totals =	$911.80		$989.0636	$989.06	$989.10	$989.00