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	$74.69	5.292%	$78.6426	$78.64	$78.65	$78.60
Purchase #2	$215.62	12.199%	$241.9235	$241.92	$241.90	$241.90
Purchase #3	$51.58	9.597%	$56.5301	$56.53	$56.55	$56.50
Purchase #4	$112.27	5.149%	$118.0508	$118.05	$118.05	$118.10
Purchase #5	$18.25	6.588%	$19.4523	$19.45	$19.45	$19.50
Purchase #6	$102.96	8.603%	$111.8176	$111.82	$111.80	$111.80
Purchase #7	$75.91	13.367%	$86.0569	$86.06	$86.05	$86.10
7 purchase totals =	$651.28		$712.4738	$712.47	$712.45	$712.50