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	$27.89	13.867%	$31.7575	$31.76	$31.75	$31.80
Purchase #2	$101.53	7.464%	$109.1082	$109.11	$109.10	$109.10
Purchase #3	$143.35	10.341%	$158.1738	$158.17	$158.15	$158.20
Purchase #4	$11.45	8.862%	$12.4647	$12.46	$12.45	$12.50
Purchase #5	$80.52	6.536%	$85.7828	$85.78	$85.80	$85.80
Purchase #6	$145.52	5.250%	$153.1598	$153.16	$153.15	$153.20
Purchase #7	$208.54	8.639%	$226.5558	$226.56	$226.55	$226.60
7 purchase totals =	$718.80		$777.0026	$777.00	$776.95	$777.20