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	$20.78	3.248%	$21.4549	$21.45	$21.45	$21.50
Purchase #2	$81.45	9.342%	$89.0591	$89.06	$89.05	$89.10
Purchase #3	$46.63	13.378%	$52.8682	$52.87	$52.85	$52.90
Purchase #4	$120.36	5.215%	$126.6368	$126.64	$126.65	$126.60
Purchase #5	$35.92	12.373%	$40.3644	$40.36	$40.35	$40.40
Purchase #6	$91.31	5.816%	$96.6206	$96.62	$96.60	$96.60
Purchase #7	$86.26	3.162%	$88.9875	$88.99	$89.00	$89.00
7 purchase totals =	$482.71		$515.9915	$515.99	$515.95	$516.10