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	$71.70	9.483%	$78.4993	$78.50	$78.50	$78.50
Purchase #2	$151.47	4.721%	$158.6209	$158.62	$158.60	$158.60
Purchase #3	$56.67	11.356%	$63.1054	$63.11	$63.10	$63.10
Purchase #4	$81.57	11.400%	$90.869	$90.87	$90.85	$90.90
Purchase #5	$10.57	4.778%	$11.075	$11.08	$11.10	$11.10
Purchase #6	$161.54	10.641%	$178.7295	$178.73	$178.75	$178.70
Purchase #7	$115.29	7.363%	$123.7788	$123.78	$123.80	$123.80
7 purchase totals =	$648.81		$704.6779	$704.69	$704.70	$704.70