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	$9.63	4.748%	$10.0872	$10.09	$10.10	$10.10
Purchase #2	$165.28	6.640%	$176.2546	$176.25	$176.25	$176.30
Purchase #3	$53.34	12.157%	$59.8245	$59.82	$59.80	$59.80
Purchase #4	$171.39	10.768%	$189.8453	$189.85	$189.85	$189.80
Purchase #5	$149.57	13.329%	$169.5062	$169.51	$169.50	$169.50
Purchase #6	$102.61	11.698%	$114.6133	$114.61	$114.60	$114.60
Purchase #7	$154.55	7.798%	$166.6018	$166.60	$166.60	$166.60
7 purchase totals =	$806.37		$886.7329	$886.73	$886.70	$886.70