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	$105.94	11.734%	$118.371	$118.37	$118.35	$118.40
Purchase #2	$102.42	13.569%	$116.3174	$116.32	$116.30	$116.30
Purchase #3	$125.27	11.336%	$139.4706	$139.47	$139.45	$139.50
Purchase #4	$78.77	13.677%	$89.5434	$89.54	$89.55	$89.50
Purchase #5	$92.47	9.366%	$101.1307	$101.13	$101.15	$101.10
Purchase #6	$59.85	13.128%	$67.7071	$67.71	$67.70	$67.70
Purchase #7	$75.36	5.113%	$79.2132	$79.21	$79.20	$79.20
7 purchase totals =	$640.08		$711.7534	$711.75	$711.70	$711.70