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	$40.90	6.830%	$43.6935	$43.69	$43.70	$43.70
Purchase #2	$38.85	4.361%	$40.5442	$40.54	$40.55	$40.50
Purchase #3	$176.96	11.739%	$197.7333	$197.73	$197.75	$197.70
Purchase #4	$66.28	5.408%	$69.8644	$69.86	$69.85	$69.90
Purchase #5	$135.64	6.575%	$144.5583	$144.56	$144.55	$144.60
Purchase #6	$109.54	10.419%	$120.953	$120.95	$120.95	$121.00
Purchase #7	$44.92	12.664%	$50.6087	$50.61	$50.60	$50.60
7 purchase totals =	$613.09		$667.9554	$667.94	$667.95	$668.00