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	$127.35	13.178%	$144.1322	$144.13	$144.15	$144.10
Purchase #2	$68.87	10.389%	$76.0249	$76.02	$76.00	$76.00
Purchase #3	$144.80	4.163%	$150.828	$150.83	$150.85	$150.80
Purchase #4	$128.31	8.579%	$139.3177	$139.32	$139.30	$139.30
Purchase #5	$50.90	8.871%	$55.4153	$55.42	$55.40	$55.40
Purchase #6	$36.63	11.340%	$40.7838	$40.78	$40.80	$40.80
Purchase #7	$173.94	10.564%	$192.315	$192.32	$192.30	$192.30
7 purchase totals =	$730.80		$798.8169	$798.82	$798.80	$798.70