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	$20.57	6.555%	$21.9184	$21.92	$21.90	$21.90
Purchase #2	$173.51	8.518%	$188.2896	$188.29	$188.30	$188.30
Purchase #3	$170.35	10.493%	$188.2248	$188.22	$188.20	$188.20
Purchase #4	$174.34	9.113%	$190.2276	$190.23	$190.25	$190.20
Purchase #5	$42.25	9.738%	$46.3643	$46.36	$46.35	$46.40
Purchase #6	$238.57	8.375%	$258.5502	$258.55	$258.55	$258.60
Purchase #7	$120.28	9.420%	$131.6104	$131.61	$131.60	$131.60
7 purchase totals =	$939.87		$1,025.1853	$1,025.18	$1,025.15	$1,025.20