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	$216.60	6.819%	$231.37	$231.37	$231.35	$231.40
Purchase #2	$167.48	6.342%	$178.1016	$178.10	$178.10	$178.10
Purchase #3	$58.99	11.282%	$65.6453	$65.65	$65.65	$65.60
Purchase #4	$183.43	7.536%	$197.2533	$197.25	$197.25	$197.30
Purchase #5	$111.83	10.712%	$123.8092	$123.81	$123.80	$123.80
Purchase #6	$87.66	13.776%	$99.736	$99.74	$99.75	$99.70
Purchase #7	$42.47	3.376%	$43.9038	$43.90	$43.90	$43.90
7 purchase totals =	$868.46		$939.8192	$939.82	$939.80	$939.80