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	$9.49	9.457%	$10.3875	$10.39	$10.40	$10.40
Purchase #2	$79.29	9.697%	$86.9788	$86.98	$87.00	$87.00
Purchase #3	$154.90	11.233%	$172.2999	$172.30	$172.30	$172.30
Purchase #4	$122.78	6.200%	$130.3924	$130.39	$130.40	$130.40
Purchase #5	$112.94	7.530%	$121.4444	$121.44	$121.45	$121.40
Purchase #6	$69.91	12.108%	$78.3747	$78.37	$78.35	$78.40
Purchase #7	$189.28	13.860%	$215.5142	$215.51	$215.50	$215.50
7 purchase totals =	$738.59		$815.3919	$815.38	$815.40	$815.40