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	$116.99	8.680%	$127.1447	$127.14	$127.15	$127.10
Purchase #2	$205.77	3.502%	$212.9761	$212.98	$213.00	$213.00
Purchase #3	$27.71	7.872%	$29.8913	$29.89	$29.90	$29.90
Purchase #4	$34.71	12.850%	$39.1702	$39.17	$39.15	$39.20
Purchase #5	$89.66	5.537%	$94.6245	$94.62	$94.60	$94.60
Purchase #6	$76.78	5.373%	$80.9054	$80.91	$80.90	$80.90
Purchase #7	$47.66	13.755%	$54.2156	$54.22	$54.20	$54.20
7 purchase totals =	$599.28		$638.9278	$638.93	$638.90	$638.90