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	$29.55	9.762%	$32.4347	$32.43	$32.45	$32.40
Purchase #2	$81.57	7.732%	$87.877	$87.88	$87.90	$87.90
Purchase #3	$30.50	3.707%	$31.6306	$31.63	$31.65	$31.60
Purchase #4	$145.53	4.361%	$151.8766	$151.88	$151.90	$151.90
Purchase #5	$77.94	3.627%	$80.7669	$80.77	$80.75	$80.80
Purchase #6	$99.94	5.661%	$105.5976	$105.60	$105.60	$105.60
Purchase #7	$81.90	13.771%	$93.1784	$93.18	$93.20	$93.20
7 purchase totals =	$546.93		$583.3618	$583.37	$583.45	$583.40