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	$62.78	11.767%	$70.1673	$70.17	$70.15	$70.20
Purchase #2	$215.34	3.418%	$222.7003	$222.70	$222.70	$222.70
Purchase #3	$140.92	3.679%	$146.1044	$146.10	$146.10	$146.10
Purchase #4	$231.80	7.240%	$248.5823	$248.58	$248.60	$248.60
Purchase #5	$235.71	5.446%	$248.5468	$248.55	$248.55	$248.50
Purchase #6	$52.45	7.839%	$56.5616	$56.56	$56.55	$56.60
Purchase #7	$80.98	11.591%	$90.3664	$90.37	$90.35	$90.40
7 purchase totals =	$1,019.98		$1,083.0291	$1,083.03	$1,083.00	$1,083.10