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	$61.83	5.235%	$65.0668	$65.07	$65.05	$65.10
Purchase #2	$138.46	9.287%	$151.3188	$151.32	$151.30	$151.30
Purchase #3	$27.76	13.508%	$31.5098	$31.51	$31.50	$31.50
Purchase #4	$48.88	6.561%	$52.087	$52.09	$52.10	$52.10
Purchase #5	$122.50	4.241%	$127.6952	$127.70	$127.70	$127.70
Purchase #6	$167.25	6.594%	$178.2785	$178.28	$178.30	$178.30
Purchase #7	$34.71	12.662%	$39.105	$39.11	$39.10	$39.10
7 purchase totals =	$601.39		$645.0611	$645.08	$645.05	$645.10