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	$41.91	3.697%	$43.4594	$43.46	$43.45	$43.50
Purchase #2	$156.46	10.491%	$172.8742	$172.87	$172.85	$172.90
Purchase #3	$177.33	11.808%	$198.2691	$198.27	$198.25	$198.30
Purchase #4	$82.91	3.451%	$85.7712	$85.77	$85.75	$85.80
Purchase #5	$33.97	12.701%	$38.2845	$38.28	$38.30	$38.30
Purchase #6	$222.36	4.282%	$231.8815	$231.88	$231.90	$231.90
Purchase #7	$129.70	6.503%	$138.1344	$138.13	$138.15	$138.10
7 purchase totals =	$844.64		$908.6743	$908.66	$908.65	$908.80