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	$203.97	13.840%	$232.1994	$232.20	$232.20	$232.20
Purchase #2	$115.75	4.607%	$121.0826	$121.08	$121.10	$121.10
Purchase #3	$164.41	13.186%	$186.0891	$186.09	$186.10	$186.10
Purchase #4	$99.79	11.733%	$111.4984	$111.50	$111.50	$111.50
Purchase #5	$243.58	5.292%	$256.4703	$256.47	$256.45	$256.50
Purchase #6	$91.82	9.293%	$100.3528	$100.35	$100.35	$100.40
Purchase #7	$88.89	4.737%	$93.1007	$93.10	$93.10	$93.10
7 purchase totals =	$1,008.21		$1,100.7933	$1,100.79	$1,100.80	$1,100.90