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	$38.39	3.123%	$39.5889	$39.59	$39.60	$39.60
Purchase #2	$59.98	3.291%	$61.9539	$61.95	$61.95	$62.00
Purchase #3	$218.76	3.372%	$226.1366	$226.14	$226.15	$226.10
Purchase #4	$57.56	13.128%	$65.1165	$65.12	$65.10	$65.10
Purchase #5	$109.77	9.329%	$120.0104	$120.01	$120.00	$120.00
Purchase #6	$69.59	12.707%	$78.4328	$78.43	$78.45	$78.40
Purchase #7	$170.81	11.104%	$189.7767	$189.78	$189.80	$189.80
7 purchase totals =	$724.86		$781.0158	$781.02	$781.05	$781.00