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	$15.73	11.409%	$17.5246	$17.52	$17.50	$17.50
Purchase #2	$110.99	3.116%	$114.4484	$114.45	$114.45	$114.40
Purchase #3	$151.86	4.394%	$158.5327	$158.53	$158.55	$158.50
Purchase #4	$87.66	13.747%	$99.7106	$99.71	$99.70	$99.70
Purchase #5	$40.62	5.392%	$42.8102	$42.81	$42.80	$42.80
Purchase #6	$100.45	3.287%	$103.7518	$103.75	$103.75	$103.80
Purchase #7	$174.32	5.863%	$184.5404	$184.54	$184.55	$184.50
7 purchase totals =	$681.63		$721.3187	$721.31	$721.30	$721.20