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	$30.77	4.441%	$32.1365	$32.14	$32.15	$32.10
Purchase #2	$139.65	11.640%	$155.9053	$155.91	$155.90	$155.90
Purchase #3	$52.87	9.664%	$57.9794	$57.98	$58.00	$58.00
Purchase #4	$243.79	5.194%	$256.4525	$256.45	$256.45	$256.50
Purchase #5	$142.85	5.753%	$151.0682	$151.07	$151.05	$151.10
Purchase #6	$78.70	8.799%	$85.6248	$85.62	$85.60	$85.60
Purchase #7	$214.98	10.755%	$238.1011	$238.10	$238.10	$238.10
7 purchase totals =	$903.61		$977.2678	$977.27	$977.25	$977.30