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	$26.35	6.611%	$28.092	$28.09	$28.10	$28.10
Purchase #2	$90.47	11.527%	$100.8985	$100.90	$100.90	$100.90
Purchase #3	$32.79	7.242%	$35.1647	$35.16	$35.15	$35.20
Purchase #4	$245.55	13.649%	$279.0651	$279.07	$279.05	$279.10
Purchase #5	$24.89	9.116%	$27.159	$27.16	$27.15	$27.20
Purchase #6	$39.50	8.262%	$42.7635	$42.76	$42.75	$42.80
Purchase #7	$46.51	9.627%	$50.9875	$50.99	$51.00	$51.00
7 purchase totals =	$506.06		$564.1303	$564.13	$564.10	$564.30