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	$164.43	12.722%	$185.3488	$185.35	$185.35	$185.30
Purchase #2	$149.42	10.367%	$164.9104	$164.91	$164.90	$164.90
Purchase #3	$20.69	5.815%	$21.8931	$21.89	$21.90	$21.90
Purchase #4	$239.56	11.260%	$266.5345	$266.53	$266.55	$266.50
Purchase #5	$32.45	8.546%	$35.2232	$35.22	$35.20	$35.20
Purchase #6	$14.32	5.720%	$15.1391	$15.14	$15.15	$15.10
Purchase #7	$95.34	5.808%	$100.8773	$100.88	$100.90	$100.90
7 purchase totals =	$716.21		$789.9264	$789.92	$789.95	$789.80