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	$10.51	9.412%	$11.4992	$11.50	$11.50	$11.50
Purchase #2	$99.71	6.659%	$106.3497	$106.35	$106.35	$106.30
Purchase #3	$207.80	7.663%	$223.7237	$223.72	$223.70	$223.70
Purchase #4	$98.85	11.134%	$109.856	$109.86	$109.85	$109.90
Purchase #5	$90.70	13.140%	$102.618	$102.62	$102.60	$102.60
Purchase #6	$49.40	5.530%	$52.1318	$52.13	$52.15	$52.10
Purchase #7	$163.52	10.302%	$180.3658	$180.37	$180.35	$180.40
7 purchase totals =	$720.49		$786.5442	$786.55	$786.50	$786.50