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	$53.80	9.667%	$59.0008	$59.00	$59.00	$59.00
Purchase #2	$184.98	10.683%	$204.7414	$204.74	$204.75	$204.70
Purchase #3	$218.35	9.204%	$238.4469	$238.45	$238.45	$238.40
Purchase #4	$207.65	12.239%	$233.0643	$233.06	$233.05	$233.10
Purchase #5	$6.62	13.296%	$7.5002	$7.50	$7.50	$7.50
Purchase #6	$215.61	6.800%	$230.2715	$230.27	$230.25	$230.30
Purchase #7	$43.79	4.153%	$45.6086	$45.61	$45.60	$45.60
7 purchase totals =	$930.80		$1,018.6337	$1,018.63	$1,018.60	$1,018.60