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	$210.69	3.414%	$217.883	$217.88	$217.90	$217.90
Purchase #2	$153.98	3.464%	$159.3139	$159.31	$159.30	$159.30
Purchase #3	$201.82	13.711%	$229.4915	$229.49	$229.50	$229.50
Purchase #4	$173.41	13.493%	$196.8082	$196.81	$196.80	$196.80
Purchase #5	$240.94	10.434%	$266.0797	$266.08	$266.10	$266.10
Purchase #6	$49.55	6.509%	$52.7752	$52.78	$52.80	$52.80
Purchase #7	$92.57	3.611%	$95.9127	$95.91	$95.90	$95.90
7 purchase totals =	$1,122.96		$1,218.2642	$1,218.26	$1,218.30	$1,218.30