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	$114.98	8.283%	$124.5038	$124.50	$124.50	$124.50
Purchase #2	$158.25	8.126%	$171.1094	$171.11	$171.10	$171.10
Purchase #3	$96.27	6.339%	$102.3726	$102.37	$102.35	$102.40
Purchase #4	$76.37	4.763%	$80.0075	$80.01	$80.00	$80.00
Purchase #5	$192.59	6.757%	$205.6033	$205.60	$205.60	$205.60
Purchase #6	$98.97	12.586%	$111.4264	$111.43	$111.45	$111.40
Purchase #7	$45.27	9.420%	$49.5344	$49.53	$49.55	$49.50
7 purchase totals =	$782.70		$844.5574	$844.55	$844.55	$844.50