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	$35.62	9.691%	$39.0719	$39.07	$39.05	$39.10
Purchase #2	$184.78	8.380%	$200.2646	$200.26	$200.25	$200.30
Purchase #3	$128.86	12.786%	$145.336	$145.34	$145.35	$145.30
Purchase #4	$128.64	3.844%	$133.5849	$133.58	$133.60	$133.60
Purchase #5	$32.36	6.364%	$34.4194	$34.42	$34.40	$34.40
Purchase #6	$163.88	5.244%	$172.4739	$172.47	$172.45	$172.50
Purchase #7	$67.84	6.280%	$72.1004	$72.10	$72.10	$72.10
7 purchase totals =	$741.98		$797.2511	$797.24	$797.20	$797.30