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	$25.87	7.129%	$27.7143	$27.71	$27.70	$27.70
Purchase #2	$82.66	9.441%	$90.4639	$90.46	$90.45	$90.50
Purchase #3	$77.29	5.477%	$81.5232	$81.52	$81.50	$81.50
Purchase #4	$13.39	3.209%	$13.8197	$13.82	$13.80	$13.80
Purchase #5	$180.45	5.289%	$189.994	$189.99	$190.00	$190.00
Purchase #6	$223.63	10.524%	$247.1648	$247.16	$247.15	$247.20
Purchase #7	$66.78	7.610%	$71.862	$71.86	$71.85	$71.90
7 purchase totals =	$670.07		$722.5419	$722.52	$722.45	$722.60