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	$96.93	3.768%	$100.5823	$100.58	$100.60	$100.60
Purchase #2	$231.70	6.715%	$247.2587	$247.26	$247.25	$247.30
Purchase #3	$105.96	7.310%	$113.7057	$113.71	$113.70	$113.70
Purchase #4	$84.57	6.492%	$90.0603	$90.06	$90.05	$90.10
Purchase #5	$41.58	5.398%	$43.8245	$43.82	$43.80	$43.80
Purchase #6	$38.74	12.751%	$43.6797	$43.68	$43.70	$43.70
Purchase #7	$66.29	8.237%	$71.7503	$71.75	$71.75	$71.80
7 purchase totals =	$665.77		$710.8615	$710.86	$710.85	$711.00