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	$136.64	9.793%	$150.0212	$150.02	$150.00	$150.00
Purchase #2	$46.89	10.466%	$51.7975	$51.80	$51.80	$51.80
Purchase #3	$59.95	6.188%	$63.6597	$63.66	$63.65	$63.70
Purchase #4	$53.87	4.461%	$56.2731	$56.27	$56.25	$56.30
Purchase #5	$242.26	5.352%	$255.2258	$255.23	$255.25	$255.20
Purchase #6	$47.95	4.461%	$50.089	$50.09	$50.10	$50.10
Purchase #7	$39.53	3.493%	$40.9108	$40.91	$40.90	$40.90
7 purchase totals =	$627.09		$667.9771	$667.98	$667.95	$668.00