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	$22.58	6.867%	$24.1306	$24.13	$24.15	$24.10
Purchase #2	$10.82	6.521%	$11.5256	$11.53	$11.55	$11.50
Purchase #3	$82.84	8.830%	$90.1548	$90.15	$90.15	$90.20
Purchase #4	$116.70	4.418%	$121.8558	$121.86	$121.85	$121.90
Purchase #5	$30.93	11.619%	$34.5238	$34.52	$34.50	$34.50
Purchase #6	$80.27	6.744%	$85.6834	$85.68	$85.70	$85.70
Purchase #7	$31.62	7.584%	$34.0181	$34.02	$34.00	$34.00
7 purchase totals =	$375.76		$401.8921	$401.89	$401.90	$401.90