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	$155.81	13.766%	$177.2588	$177.26	$177.25	$177.30
Purchase #2	$89.38	9.456%	$97.8318	$97.83	$97.85	$97.80
Purchase #3	$74.85	6.846%	$79.9742	$79.97	$79.95	$80.00
Purchase #4	$41.89	9.871%	$46.025	$46.03	$46.05	$46.00
Purchase #5	$128.89	11.473%	$143.6775	$143.68	$143.70	$143.70
Purchase #6	$70.65	10.755%	$78.2484	$78.25	$78.25	$78.20
Purchase #7	$85.99	5.268%	$90.52	$90.52	$90.50	$90.50
7 purchase totals =	$647.46		$713.5357	$713.54	$713.55	$713.50