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	$18.68	13.149%	$21.1362	$21.14	$21.15	$21.10
Purchase #2	$135.99	13.152%	$153.8754	$153.88	$153.90	$153.90
Purchase #3	$139.72	11.628%	$155.9666	$155.97	$155.95	$156.00
Purchase #4	$87.94	12.826%	$99.2192	$99.22	$99.20	$99.20
Purchase #5	$28.29	5.713%	$29.9062	$29.91	$29.90	$29.90
Purchase #6	$190.69	5.104%	$200.4228	$200.42	$200.40	$200.40
Purchase #7	$30.74	5.218%	$32.344	$32.34	$32.35	$32.30
7 purchase totals =	$632.05		$692.8704	$692.88	$692.85	$692.80