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	$141.72	10.443%	$156.5198	$156.52	$156.50	$156.50
Purchase #2	$116.86	11.794%	$130.6425	$130.64	$130.65	$130.60
Purchase #3	$154.48	12.569%	$173.8966	$173.90	$173.90	$173.90
Purchase #4	$63.77	8.487%	$69.1822	$69.18	$69.20	$69.20
Purchase #5	$78.39	6.377%	$83.3889	$83.39	$83.40	$83.40
Purchase #6	$100.91	8.792%	$109.782	$109.78	$109.80	$109.80
Purchase #7	$86.78	9.374%	$94.9148	$94.91	$94.90	$94.90
7 purchase totals =	$742.91		$818.3268	$818.32	$818.35	$818.30