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	$216.49	4.540%	$226.3186	$226.32	$226.30	$226.30
Purchase #2	$175.45	8.648%	$190.6229	$190.62	$190.60	$190.60
Purchase #3	$245.92	10.852%	$272.6072	$272.61	$272.60	$272.60
Purchase #4	$149.78	5.845%	$158.5346	$158.53	$158.55	$158.50
Purchase #5	$145.41	13.348%	$164.8193	$164.82	$164.80	$164.80
Purchase #6	$229.73	6.425%	$244.4902	$244.49	$244.50	$244.50
Purchase #7	$64.54	3.118%	$66.5524	$66.55	$66.55	$66.60
7 purchase totals =	$1,227.32		$1,323.9452	$1,323.94	$1,323.90	$1,323.90