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	$108.57	13.602%	$123.3377	$123.34	$123.35	$123.30
Purchase #2	$43.76	8.633%	$47.5378	$47.54	$47.55	$47.50
Purchase #3	$38.44	7.667%	$41.3872	$41.39	$41.40	$41.40
Purchase #4	$46.53	8.420%	$50.4478	$50.45	$50.45	$50.40
Purchase #5	$60.73	6.401%	$64.6173	$64.62	$64.60	$64.60
Purchase #6	$138.70	12.753%	$156.3884	$156.39	$156.40	$156.40
Purchase #7	$90.56	13.116%	$102.4378	$102.44	$102.45	$102.40
7 purchase totals =	$527.29		$586.1540	$586.17	$586.20	$586.00