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	$35.94	4.856%	$37.6852	$37.69	$37.70	$37.70
Purchase #2	$45.92	13.396%	$52.0714	$52.07	$52.05	$52.10
Purchase #3	$70.98	10.172%	$78.2001	$78.20	$78.20	$78.20
Purchase #4	$151.70	8.725%	$164.9358	$164.94	$164.95	$164.90
Purchase #5	$233.38	8.288%	$252.7225	$252.72	$252.70	$252.70
Purchase #6	$27.81	13.578%	$31.586	$31.59	$31.60	$31.60
Purchase #7	$46.73	9.415%	$51.1296	$51.13	$51.15	$51.10
7 purchase totals =	$612.46		$668.3306	$668.34	$668.35	$668.30