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	$7.43	12.277%	$8.3422	$8.34	$8.35	$8.30
Purchase #2	$154.84	9.531%	$169.5978	$169.60	$169.60	$169.60
Purchase #3	$35.47	6.847%	$37.8986	$37.90	$37.90	$37.90
Purchase #4	$111.60	6.568%	$118.9299	$118.93	$118.95	$118.90
Purchase #5	$10.91	10.644%	$12.0713	$12.07	$12.05	$12.10
Purchase #6	$83.95	12.589%	$94.5185	$94.52	$94.50	$94.50
Purchase #7	$156.81	10.660%	$173.5259	$173.53	$173.55	$173.50
7 purchase totals =	$561.01		$614.8842	$614.89	$614.90	$614.80