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	$73.70	5.448%	$77.7152	$77.72	$77.70	$77.70
Purchase #2	$164.48	11.628%	$183.6057	$183.61	$183.60	$183.60
Purchase #3	$184.98	6.144%	$196.3452	$196.35	$196.35	$196.30
Purchase #4	$133.36	7.104%	$142.8339	$142.83	$142.85	$142.80
Purchase #5	$15.86	9.245%	$17.3263	$17.33	$17.35	$17.30
Purchase #6	$116.40	6.660%	$124.1522	$124.15	$124.15	$124.20
Purchase #7	$29.59	7.515%	$31.8137	$31.81	$31.80	$31.80
7 purchase totals =	$718.37		$773.7922	$773.80	$773.80	$773.70