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	$82.75	4.230%	$86.2503	$86.25	$86.25	$86.30
Purchase #2	$239.35	13.248%	$271.0591	$271.06	$271.05	$271.10
Purchase #3	$19.47	13.707%	$22.1388	$22.14	$22.15	$22.10
Purchase #4	$241.57	5.857%	$255.7188	$255.72	$255.70	$255.70
Purchase #5	$51.50	10.426%	$56.8694	$56.87	$56.85	$56.90
Purchase #6	$84.31	5.772%	$89.1764	$89.18	$89.20	$89.20
Purchase #7	$29.97	4.132%	$31.2084	$31.21	$31.20	$31.20
7 purchase totals =	$748.92		$812.4212	$812.43	$812.40	$812.50