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	$137.48	10.850%	$152.3966	$152.40	$152.40	$152.40
Purchase #2	$73.72	4.680%	$77.1701	$77.17	$77.15	$77.20
Purchase #3	$222.53	3.839%	$231.0729	$231.07	$231.05	$231.10
Purchase #4	$10.92	13.300%	$12.3724	$12.37	$12.35	$12.40
Purchase #5	$183.96	13.389%	$208.5904	$208.59	$208.60	$208.60
Purchase #6	$196.37	10.669%	$217.3207	$217.32	$217.30	$217.30
Purchase #7	$219.98	9.570%	$241.0321	$241.03	$241.05	$241.00
7 purchase totals =	$1,044.96		$1,139.9552	$1,139.95	$1,139.90	$1,140.00