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	$99.46	9.752%	$109.1593	$109.16	$109.15	$109.20
Purchase #2	$229.34	7.200%	$245.8525	$245.85	$245.85	$245.90
Purchase #3	$226.40	3.116%	$233.4546	$233.45	$233.45	$233.50
Purchase #4	$183.97	3.283%	$190.0097	$190.01	$190.00	$190.00
Purchase #5	$57.98	8.470%	$62.8909	$62.89	$62.90	$62.90
Purchase #6	$59.97	12.209%	$67.2917	$67.29	$67.30	$67.30
Purchase #7	$76.46	7.808%	$82.43	$82.43	$82.45	$82.40
7 purchase totals =	$933.58		$991.0887	$991.08	$991.10	$991.20