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	$227.81	9.665%	$249.8278	$249.83	$249.85	$249.80
Purchase #2	$65.98	7.522%	$70.943	$70.94	$70.95	$70.90
Purchase #3	$18.55	5.434%	$19.558	$19.56	$19.55	$19.60
Purchase #4	$54.64	5.574%	$57.6856	$57.69	$57.70	$57.70
Purchase #5	$162.78	6.159%	$172.8056	$172.81	$172.80	$172.80
Purchase #6	$50.32	10.773%	$55.741	$55.74	$55.75	$55.70
Purchase #7	$229.93	11.631%	$256.6732	$256.67	$256.65	$256.70
7 purchase totals =	$810.01		$883.2342	$883.24	$883.25	$883.20