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	$38.40	5.817%	$40.6337	$40.63	$40.65	$40.60
Purchase #2	$140.75	3.261%	$145.3399	$145.34	$145.35	$145.30
Purchase #3	$224.62	13.693%	$255.3772	$255.38	$255.40	$255.40
Purchase #4	$120.28	5.564%	$126.9724	$126.97	$126.95	$127.00
Purchase #5	$209.63	6.227%	$222.6837	$222.68	$222.70	$222.70
Purchase #6	$79.68	13.196%	$90.1946	$90.19	$90.20	$90.20
Purchase #7	$19.86	6.518%	$21.1545	$21.15	$21.15	$21.20
7 purchase totals =	$833.22		$902.3560	$902.34	$902.40	$902.40