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	$118.81	8.566%	$128.9873	$128.99	$129.00	$129.00
Purchase #2	$152.37	11.336%	$169.6427	$169.64	$169.65	$169.60
Purchase #3	$91.37	9.821%	$100.3434	$100.34	$100.35	$100.30
Purchase #4	$38.84	11.522%	$43.3151	$43.32	$43.30	$43.30
Purchase #5	$224.29	10.716%	$248.3249	$248.32	$248.30	$248.30
Purchase #6	$164.85	4.823%	$172.8007	$172.80	$172.80	$172.80
Purchase #7	$85.90	10.272%	$94.7236	$94.72	$94.70	$94.70
7 purchase totals =	$876.43		$958.1377	$958.13	$958.10	$958.00