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	$236.60	12.729%	$266.7168	$266.72	$266.70	$266.70
Purchase #2	$240.28	12.739%	$270.8893	$270.89	$270.90	$270.90
Purchase #3	$109.42	10.836%	$121.2768	$121.28	$121.30	$121.30
Purchase #4	$185.61	10.507%	$205.112	$205.11	$205.10	$205.10
Purchase #5	$70.31	11.607%	$78.4709	$78.47	$78.45	$78.50
Purchase #6	$86.59	12.855%	$97.7211	$97.72	$97.70	$97.70
Purchase #7	$219.62	9.870%	$241.2965	$241.30	$241.30	$241.30
7 purchase totals =	$1,148.43		$1,281.4834	$1,281.49	$1,281.45	$1,281.50