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	$61.89	9.209%	$67.5895	$67.59	$67.60	$67.60
Purchase #2	$119.92	5.496%	$126.5108	$126.51	$126.50	$126.50
Purchase #3	$64.61	7.733%	$69.6063	$69.61	$69.60	$69.60
Purchase #4	$34.47	4.204%	$35.9191	$35.92	$35.90	$35.90
Purchase #5	$216.91	4.258%	$226.146	$226.15	$226.15	$226.10
Purchase #6	$7.73	5.528%	$8.1573	$8.16	$8.15	$8.20
Purchase #7	$98.81	6.504%	$105.2366	$105.24	$105.25	$105.20
7 purchase totals =	$604.34		$639.1656	$639.18	$639.15	$639.10