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	$61.91	5.535%	$65.3367	$65.34	$65.35	$65.30
Purchase #2	$176.86	11.293%	$196.8328	$196.83	$196.85	$196.80
Purchase #3	$186.53	9.767%	$204.7484	$204.75	$204.75	$204.70
Purchase #4	$118.54	6.654%	$126.4277	$126.43	$126.45	$126.40
Purchase #5	$37.61	6.839%	$40.1821	$40.18	$40.20	$40.20
Purchase #6	$144.88	11.456%	$161.4775	$161.48	$161.50	$161.50
Purchase #7	$119.81	10.212%	$132.045	$132.05	$132.05	$132.00
7 purchase totals =	$846.14		$927.0502	$927.06	$927.15	$926.90