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	$158.90	5.733%	$168.0097	$168.01	$168.00	$168.00
Purchase #2	$160.36	7.206%	$171.9155	$171.92	$171.90	$171.90
Purchase #3	$15.43	7.215%	$16.5433	$16.54	$16.55	$16.50
Purchase #4	$107.29	10.754%	$118.828	$118.83	$118.85	$118.80
Purchase #5	$80.74	12.134%	$90.537	$90.54	$90.55	$90.50
Purchase #6	$182.60	5.412%	$192.4823	$192.48	$192.50	$192.50
Purchase #7	$12.45	3.165%	$12.844	$12.84	$12.85	$12.80
7 purchase totals =	$717.77		$771.1598	$771.16	$771.20	$771.00