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	$83.84	7.579%	$90.1942	$90.19	$90.20	$90.20
Purchase #2	$56.67	10.672%	$62.7178	$62.72	$62.70	$62.70
Purchase #3	$186.65	12.140%	$209.3093	$209.31	$209.30	$209.30
Purchase #4	$144.28	11.553%	$160.9487	$160.95	$160.95	$160.90
Purchase #5	$21.77	4.302%	$22.7065	$22.71	$22.70	$22.70
Purchase #6	$145.89	5.730%	$154.2495	$154.25	$154.25	$154.20
Purchase #7	$205.46	13.357%	$232.9033	$232.90	$232.90	$232.90
7 purchase totals =	$844.56		$933.0293	$933.03	$933.00	$932.90