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	$8.89	7.698%	$9.5744	$9.57	$9.55	$9.60
Purchase #2	$169.76	9.744%	$186.3014	$186.30	$186.30	$186.30
Purchase #3	$50.64	11.614%	$56.5213	$56.52	$56.50	$56.50
Purchase #4	$93.68	6.306%	$99.5875	$99.59	$99.60	$99.60
Purchase #5	$123.76	6.154%	$131.3762	$131.38	$131.40	$131.40
Purchase #6	$168.85	8.252%	$182.7835	$182.78	$182.80	$182.80
Purchase #7	$34.51	11.431%	$38.4548	$38.45	$38.45	$38.50
7 purchase totals =	$650.09		$704.5991	$704.59	$704.60	$704.70