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	$148.25	7.326%	$159.1108	$159.11	$159.10	$159.10
Purchase #2	$223.83	6.698%	$238.8221	$238.82	$238.80	$238.80
Purchase #3	$228.83	5.712%	$241.9008	$241.90	$241.90	$241.90
Purchase #4	$112.47	12.450%	$126.4725	$126.47	$126.45	$126.50
Purchase #5	$171.98	4.774%	$180.1903	$180.19	$180.20	$180.20
Purchase #6	$124.39	7.141%	$133.2727	$133.27	$133.25	$133.30
Purchase #7	$126.81	12.787%	$143.0252	$143.03	$143.05	$143.00
7 purchase totals =	$1,136.56		$1,222.7944	$1,222.79	$1,222.75	$1,222.80