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	$54.75	7.687%	$58.9586	$58.96	$58.95	$59.00
Purchase #2	$141.78	3.176%	$146.2829	$146.28	$146.30	$146.30
Purchase #3	$54.52	13.407%	$61.8295	$61.83	$61.85	$61.80
Purchase #4	$11.43	7.626%	$12.3017	$12.30	$12.30	$12.30
Purchase #5	$24.93	7.698%	$26.8491	$26.85	$26.85	$26.80
Purchase #6	$117.50	8.798%	$127.8377	$127.84	$127.85	$127.80
Purchase #7	$79.77	7.604%	$85.8357	$85.84	$85.85	$85.80
7 purchase totals =	$484.68		$519.8952	$519.90	$519.95	$519.80