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	$92.50	8.126%	$100.0166	$100.02	$100.00	$100.00
Purchase #2	$238.65	9.111%	$260.3934	$260.39	$260.40	$260.40
Purchase #3	$57.98	12.447%	$65.1968	$65.20	$65.20	$65.20
Purchase #4	$126.25	9.357%	$138.0632	$138.06	$138.05	$138.10
Purchase #5	$228.52	4.521%	$238.8514	$238.85	$238.85	$238.90
Purchase #6	$126.57	10.199%	$139.4789	$139.48	$139.50	$139.50
Purchase #7	$96.67	6.866%	$103.3074	$103.31	$103.30	$103.30
7 purchase totals =	$967.14		$1,045.3077	$1,045.31	$1,045.30	$1,045.40