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	$138.84	4.742%	$145.4238	$145.42	$145.40	$145.40
Purchase #2	$53.96	5.576%	$56.9688	$56.97	$56.95	$57.00
Purchase #3	$238.39	7.519%	$256.3145	$256.31	$256.30	$256.30
Purchase #4	$114.78	7.792%	$123.7237	$123.72	$123.70	$123.70
Purchase #5	$30.95	9.874%	$34.006	$34.01	$34.00	$34.00
Purchase #6	$199.98	4.460%	$208.8991	$208.90	$208.90	$208.90
Purchase #7	$154.50	12.526%	$173.8527	$173.85	$173.85	$173.90
7 purchase totals =	$931.40		$999.1886	$999.18	$999.10	$999.20