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	$137.86	12.815%	$155.5268	$155.53	$155.55	$155.50
Purchase #2	$168.93	9.625%	$185.1895	$185.19	$185.20	$185.20
Purchase #3	$12.67	9.409%	$13.8621	$13.86	$13.85	$13.90
Purchase #4	$54.43	3.125%	$56.1309	$56.13	$56.15	$56.10
Purchase #5	$81.62	9.275%	$89.1903	$89.19	$89.20	$89.20
Purchase #6	$51.38	10.297%	$56.6706	$56.67	$56.65	$56.70
Purchase #7	$9.61	3.856%	$9.9806	$9.98	$10.00	$10.00
7 purchase totals =	$516.50		$566.5508	$566.55	$566.60	$566.60