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	$126.60	7.803%	$136.4786	$136.48	$136.50	$136.50
Purchase #2	$130.25	9.324%	$142.3945	$142.39	$142.40	$142.40
Purchase #3	$111.75	10.110%	$123.0479	$123.05	$123.05	$123.00
Purchase #4	$242.83	5.560%	$256.3313	$256.33	$256.35	$256.30
Purchase #5	$118.69	13.380%	$134.5707	$134.57	$134.55	$134.60
Purchase #6	$7.29	8.351%	$7.8988	$7.90	$7.90	$7.90
Purchase #7	$94.56	11.233%	$105.1819	$105.18	$105.20	$105.20
7 purchase totals =	$831.97		$905.9037	$905.90	$905.95	$905.90