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	$33.93	6.116%	$36.0052	$36.01	$36.00	$36.00
Purchase #2	$108.60	7.776%	$117.0447	$117.04	$117.05	$117.00
Purchase #3	$80.86	7.500%	$86.9245	$86.92	$86.90	$86.90
Purchase #4	$105.37	5.746%	$111.4246	$111.42	$111.40	$111.40
Purchase #5	$32.55	4.384%	$33.977	$33.98	$34.00	$34.00
Purchase #6	$34.53	8.524%	$37.4733	$37.47	$37.45	$37.50
Purchase #7	$119.36	9.804%	$131.0621	$131.06	$131.05	$131.10
7 purchase totals =	$515.20		$553.9114	$553.90	$553.85	$553.90