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	$47.31	13.119%	$53.5166	$53.52	$53.50	$53.50
Purchase #2	$219.59	6.356%	$233.5471	$233.55	$233.55	$233.50
Purchase #3	$48.38	6.605%	$51.5755	$51.58	$51.60	$51.60
Purchase #4	$200.76	10.794%	$222.43	$222.43	$222.45	$222.40
Purchase #5	$73.59	11.750%	$82.2368	$82.24	$82.25	$82.20
Purchase #6	$16.41	12.448%	$18.4527	$18.45	$18.45	$18.50
Purchase #7	$15.96	12.301%	$17.9232	$17.92	$17.90	$17.90
7 purchase totals =	$622.00		$679.6819	$679.69	$679.70	$679.60