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	$103.88	6.769%	$110.9116	$110.91	$110.90	$110.90
Purchase #2	$203.57	5.746%	$215.2671	$215.27	$215.25	$215.30
Purchase #3	$87.99	12.603%	$99.0794	$99.08	$99.10	$99.10
Purchase #4	$241.83	9.274%	$264.2573	$264.26	$264.25	$264.30
Purchase #5	$94.33	6.291%	$100.2643	$100.26	$100.25	$100.30
Purchase #6	$41.31	12.816%	$46.6043	$46.60	$46.60	$46.60
Purchase #7	$122.76	12.762%	$138.4266	$138.43	$138.45	$138.40
7 purchase totals =	$895.67		$974.8106	$974.81	$974.80	$974.90