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	$232.47	10.336%	$256.4981	$256.50	$256.50	$256.50
Purchase #2	$136.64	11.796%	$152.7581	$152.76	$152.75	$152.80
Purchase #3	$72.45	12.537%	$81.5331	$81.53	$81.55	$81.50
Purchase #4	$62.78	6.495%	$66.8576	$66.86	$66.85	$66.90
Purchase #5	$50.86	5.238%	$53.524	$53.52	$53.50	$53.50
Purchase #6	$82.77	11.478%	$92.2703	$92.27	$92.25	$92.30
Purchase #7	$43.61	6.865%	$46.6038	$46.60	$46.60	$46.60
7 purchase totals =	$681.58		$750.0450	$750.04	$750.00	$750.10