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	$87.42	13.319%	$99.0635	$99.06	$99.05	$99.10
Purchase #2	$129.87	10.443%	$143.4323	$143.43	$143.45	$143.40
Purchase #3	$89.27	10.111%	$98.2961	$98.30	$98.30	$98.30
Purchase #4	$144.88	9.237%	$158.2626	$158.26	$158.25	$158.30
Purchase #5	$146.38	9.722%	$160.6111	$160.61	$160.60	$160.60
Purchase #6	$221.91	5.682%	$234.5189	$234.52	$234.50	$234.50
Purchase #7	$68.36	6.724%	$72.9565	$72.96	$72.95	$73.00
7 purchase totals =	$888.09		$967.1410	$967.14	$967.10	$967.20