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	$73.90	6.733%	$78.8757	$78.88	$78.90	$78.90
Purchase #2	$14.28	7.454%	$15.3444	$15.34	$15.35	$15.30
Purchase #3	$70.42	8.604%	$76.4789	$76.48	$76.50	$76.50
Purchase #4	$71.90	5.688%	$75.9897	$75.99	$76.00	$76.00
Purchase #5	$160.96	7.782%	$173.4859	$173.49	$173.50	$173.50
Purchase #6	$99.93	3.322%	$103.2497	$103.25	$103.25	$103.20
Purchase #7	$82.70	13.196%	$93.6131	$93.61	$93.60	$93.60
7 purchase totals =	$574.09		$617.0374	$617.04	$617.10	$617.00