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	$11.29	11.647%	$12.6049	$12.60	$12.60	$12.60
Purchase #2	$154.83	10.384%	$170.9075	$170.91	$170.90	$170.90
Purchase #3	$81.43	12.443%	$91.5623	$91.56	$91.55	$91.60
Purchase #4	$59.90	3.755%	$62.1492	$62.15	$62.15	$62.10
Purchase #5	$70.73	10.768%	$78.3462	$78.35	$78.35	$78.30
Purchase #6	$227.94	12.496%	$256.4234	$256.42	$256.40	$256.40
Purchase #7	$182.40	6.367%	$194.0134	$194.01	$194.00	$194.00
7 purchase totals =	$788.52		$866.0069	$866.00	$865.95	$865.90