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	$210.74	9.362%	$230.4695	$230.47	$230.45	$230.50
Purchase #2	$228.75	13.247%	$259.0525	$259.05	$259.05	$259.10
Purchase #3	$96.69	3.341%	$99.9204	$99.92	$99.90	$99.90
Purchase #4	$93.26	6.604%	$99.4189	$99.42	$99.40	$99.40
Purchase #5	$131.38	11.134%	$146.0078	$146.01	$146.00	$146.00
Purchase #6	$33.52	10.509%	$37.0426	$37.04	$37.05	$37.00
Purchase #7	$59.59	4.438%	$62.2346	$62.23	$62.25	$62.20
7 purchase totals =	$853.93		$934.1463	$934.14	$934.10	$934.10