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	$49.73	12.371%	$55.8821	$55.88	$55.90	$55.90
Purchase #2	$123.90	8.869%	$134.8887	$134.89	$134.90	$134.90
Purchase #3	$132.70	10.703%	$146.9029	$146.90	$146.90	$146.90
Purchase #4	$97.73	13.591%	$111.0125	$111.01	$111.00	$111.00
Purchase #5	$99.84	5.544%	$105.3751	$105.38	$105.40	$105.40
Purchase #6	$223.77	7.861%	$241.3606	$241.36	$241.35	$241.40
Purchase #7	$117.70	4.623%	$123.1413	$123.14	$123.15	$123.10
7 purchase totals =	$845.37		$918.5632	$918.56	$918.60	$918.60