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	$22.93	13.218%	$25.9609	$25.96	$25.95	$26.00
Purchase #2	$245.42	3.263%	$253.4281	$253.43	$253.45	$253.40
Purchase #3	$109.40	6.697%	$116.7265	$116.73	$116.75	$116.70
Purchase #4	$9.73	5.589%	$10.2738	$10.27	$10.25	$10.30
Purchase #5	$19.25	7.254%	$20.6464	$20.65	$20.65	$20.60
Purchase #6	$176.85	8.742%	$192.3102	$192.31	$192.30	$192.30
Purchase #7	$18.60	8.152%	$20.1163	$20.12	$20.10	$20.10
7 purchase totals =	$602.18		$639.4622	$639.47	$639.45	$639.40